diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index fdb622b..3436bb3 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -805,6 +805,8 @@
     "crypt_string.h",
     "data_rate_limiter.cc",
     "data_rate_limiter.h",
+    "deprecated/signal_thread.cc",
+    "deprecated/signal_thread.h",
     "dscp.h",
     "file_rotating_stream.cc",
     "file_rotating_stream.h",
@@ -857,7 +859,6 @@
     "rtc_certificate.h",
     "rtc_certificate_generator.cc",
     "rtc_certificate_generator.h",
-    "signal_thread.cc",
     "signal_thread.h",
     "sigslot_repeater.h",
     "socket.cc",
@@ -1308,6 +1309,7 @@
       "callback_unittest.cc",
       "crc32_unittest.cc",
       "data_rate_limiter_unittest.cc",
+      "deprecated/signal_thread_unittest.cc",
       "fake_clock_unittest.cc",
       "helpers_unittest.cc",
       "ip_address_unittest.cc",
@@ -1320,7 +1322,6 @@
       "rolling_accumulator_unittest.cc",
       "rtc_certificate_generator_unittest.cc",
       "rtc_certificate_unittest.cc",
-      "signal_thread_unittest.cc",
       "sigslot_tester_unittest.cc",
       "test_client_unittest.cc",
       "thread_unittest.cc",
diff --git a/rtc_base/signal_thread.cc b/rtc_base/deprecated/signal_thread.cc
similarity index 80%
rename from rtc_base/signal_thread.cc
rename to rtc_base/deprecated/signal_thread.cc
index 8f0d597..96bdd65 100644
--- a/rtc_base/signal_thread.cc
+++ b/rtc_base/deprecated/signal_thread.cc
@@ -8,7 +8,7 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#include "rtc_base/signal_thread.h"
+#include "rtc_base/deprecated/signal_thread.h"
 
 #include <memory>
 
@@ -23,19 +23,20 @@
 // SignalThread
 ///////////////////////////////////////////////////////////////////////////////
 
-SignalThread::SignalThread()
+DEPRECATED_SignalThread::DEPRECATED_SignalThread()
     : main_(Thread::Current()), worker_(this), state_(kInit), refcount_(1) {
-  main_->SignalQueueDestroyed.connect(this,
-                                      &SignalThread::OnMainThreadDestroyed);
+  main_->SignalQueueDestroyed.connect(
+      this, &DEPRECATED_SignalThread::OnMainThreadDestroyed);
   worker_.SetName("SignalThread", this);
 }
 
-SignalThread::~SignalThread() {
+DEPRECATED_SignalThread::~DEPRECATED_SignalThread() {
   rtc::CritScope lock(&cs_);
   RTC_DCHECK(refcount_ == 0);
 }
 
-bool SignalThread::SetName(const std::string& name, const void* obj) {
+bool DEPRECATED_SignalThread::SetName(const std::string& name,
+                                      const void* obj) {
   EnterExit ee(this);
   RTC_DCHECK(!destroy_called_);
   RTC_DCHECK(main_->IsCurrent());
@@ -43,7 +44,7 @@
   return worker_.SetName(name, obj);
 }
 
-void SignalThread::Start() {
+void DEPRECATED_SignalThread::Start() {
   EnterExit ee(this);
   RTC_DCHECK(!destroy_called_);
   RTC_DCHECK(main_->IsCurrent());
@@ -56,7 +57,7 @@
   }
 }
 
-void SignalThread::Destroy(bool wait) {
+void DEPRECATED_SignalThread::Destroy(bool wait) {
   EnterExit ee(this);
   // Sometimes the caller can't guarantee which thread will call Destroy, only
   // that it will be the last thing it does.
@@ -83,7 +84,7 @@
   }
 }
 
-void SignalThread::Release() {
+void DEPRECATED_SignalThread::Release() {
   EnterExit ee(this);
   RTC_DCHECK(!destroy_called_);
   RTC_DCHECK(main_->IsCurrent());
@@ -97,14 +98,14 @@
   }
 }
 
-bool SignalThread::ContinueWork() {
+bool DEPRECATED_SignalThread::ContinueWork() {
   EnterExit ee(this);
   RTC_DCHECK(!destroy_called_);
   RTC_DCHECK(worker_.IsCurrent());
   return worker_.ProcessMessages(0);
 }
 
-void SignalThread::OnMessage(Message* msg) {
+void DEPRECATED_SignalThread::OnMessage(Message* msg) {
   EnterExit ee(this);
   if (ST_MSG_WORKER_DONE == msg->message_id) {
     RTC_DCHECK(main_->IsCurrent());
@@ -135,21 +136,21 @@
   }
 }
 
-SignalThread::Worker::Worker(SignalThread* parent)
+DEPRECATED_SignalThread::Worker::Worker(DEPRECATED_SignalThread* parent)
     : Thread(std::make_unique<NullSocketServer>(), /*do_init=*/false),
       parent_(parent) {
   DoInit();
 }
 
-SignalThread::Worker::~Worker() {
+DEPRECATED_SignalThread::Worker::~Worker() {
   Stop();
 }
 
-void SignalThread::Worker::Run() {
+void DEPRECATED_SignalThread::Worker::Run() {
   parent_->Run();
 }
 
-void SignalThread::Run() {
+void DEPRECATED_SignalThread::Run() {
   DoWork();
   {
     EnterExit ee(this);
@@ -159,12 +160,12 @@
   }
 }
 
-void SignalThread::OnMainThreadDestroyed() {
+void DEPRECATED_SignalThread::OnMainThreadDestroyed() {
   EnterExit ee(this);
   main_ = nullptr;
 }
 
-bool SignalThread::Worker::IsProcessingMessagesForTesting() {
+bool DEPRECATED_SignalThread::Worker::IsProcessingMessagesForTesting() {
   return false;
 }
 
diff --git a/rtc_base/deprecated/signal_thread.h b/rtc_base/deprecated/signal_thread.h
new file mode 100644
index 0000000..54f2ba4
--- /dev/null
+++ b/rtc_base/deprecated/signal_thread.h
@@ -0,0 +1,166 @@
+/*
+ *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_DEPRECATED_SIGNAL_THREAD_H_
+#define RTC_BASE_DEPRECATED_SIGNAL_THREAD_H_
+
+#include <string>
+
+#include "rtc_base/checks.h"
+#include "rtc_base/constructor_magic.h"
+#include "rtc_base/critical_section.h"
+#include "rtc_base/deprecation.h"
+#include "rtc_base/message_handler.h"
+#include "rtc_base/third_party/sigslot/sigslot.h"
+#include "rtc_base/thread.h"
+#include "rtc_base/thread_annotations.h"
+
+namespace rtc {
+
+///////////////////////////////////////////////////////////////////////////////
+// NOTE: this class has been deprecated. Do not use for new code. New code
+// should use factilities exposed by api/task_queue/ instead.
+//
+// SignalThread - Base class for worker threads.  The main thread should call
+//  Start() to begin work, and then follow one of these models:
+//   Normal: Wait for SignalWorkDone, and then call Release to destroy.
+//   Cancellation: Call Release(true), to abort the worker thread.
+//   Fire-and-forget: Call Release(false), which allows the thread to run to
+//    completion, and then self-destruct without further notification.
+//   Periodic tasks: Wait for SignalWorkDone, then eventually call Start()
+//    again to repeat the task. When the instance isn't needed anymore,
+//    call Release. DoWork, OnWorkStart and OnWorkStop are called again,
+//    on a new thread.
+//  The subclass should override DoWork() to perform the background task.  By
+//   periodically calling ContinueWork(), it can check for cancellation.
+//   OnWorkStart and OnWorkDone can be overridden to do pre- or post-work
+//   tasks in the context of the main thread.
+///////////////////////////////////////////////////////////////////////////////
+
+class DEPRECATED_SignalThread : public sigslot::has_slots<>,
+                                protected MessageHandler {
+ public:
+  DEPRECATED_SignalThread();
+
+  // Context: Main Thread.  Call before Start to change the worker's name.
+  bool SetName(const std::string& name, const void* obj);
+
+  // Context: Main Thread.  Call to begin the worker thread.
+  void Start();
+
+  // Context: Main Thread.  If the worker thread is not running, deletes the
+  // object immediately.  Otherwise, asks the worker thread to abort processing,
+  // and schedules the object to be deleted once the worker exits.
+  // SignalWorkDone will not be signalled.  If wait is true, does not return
+  // until the thread is deleted.
+  void Destroy(bool wait);
+
+  // Context: Main Thread.  If the worker thread is complete, deletes the
+  // object immediately.  Otherwise, schedules the object to be deleted once
+  // the worker thread completes.  SignalWorkDone will be signalled.
+  void Release();
+
+  // Context: Main Thread.  Signalled when work is complete.
+  sigslot::signal1<DEPRECATED_SignalThread*> SignalWorkDone;
+
+  enum { ST_MSG_WORKER_DONE, ST_MSG_FIRST_AVAILABLE };
+
+ protected:
+  ~DEPRECATED_SignalThread() override;
+
+  Thread* worker() { return &worker_; }
+
+  // Context: Main Thread.  Subclass should override to do pre-work setup.
+  virtual void OnWorkStart() {}
+
+  // Context: Worker Thread.  Subclass should override to do work.
+  virtual void DoWork() = 0;
+
+  // Context: Worker Thread.  Subclass should call periodically to
+  // dispatch messages and determine if the thread should terminate.
+  bool ContinueWork();
+
+  // Context: Worker Thread.  Subclass should override when extra work is
+  // needed to abort the worker thread.
+  virtual void OnWorkStop() {}
+
+  // Context: Main Thread.  Subclass should override to do post-work cleanup.
+  virtual void OnWorkDone() {}
+
+  // Context: Any Thread.  If subclass overrides, be sure to call the base
+  // implementation.  Do not use (message_id < ST_MSG_FIRST_AVAILABLE)
+  void OnMessage(Message* msg) override;
+
+ private:
+  enum State {
+    kInit,       // Initialized, but not started
+    kRunning,    // Started and doing work
+    kReleasing,  // Same as running, but to be deleted when work is done
+    kComplete,   // Work is done
+    kStopping,   // Work is being interrupted
+  };
+
+  class Worker : public Thread {
+   public:
+    explicit Worker(DEPRECATED_SignalThread* parent);
+    ~Worker() override;
+    void Run() override;
+    bool IsProcessingMessagesForTesting() override;
+
+   private:
+    DEPRECATED_SignalThread* parent_;
+
+    RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(Worker);
+  };
+
+  class RTC_SCOPED_LOCKABLE EnterExit {
+   public:
+    explicit EnterExit(DEPRECATED_SignalThread* t)
+        RTC_EXCLUSIVE_LOCK_FUNCTION(t->cs_)
+        : t_(t) {
+      t_->cs_.Enter();
+      // If refcount_ is zero then the object has already been deleted and we
+      // will be double-deleting it in ~EnterExit()! (shouldn't happen)
+      RTC_DCHECK_NE(0, t_->refcount_);
+      ++t_->refcount_;
+    }
+    ~EnterExit() RTC_UNLOCK_FUNCTION() {
+      bool d = (0 == --t_->refcount_);
+      t_->cs_.Leave();
+      if (d)
+        delete t_;
+    }
+
+   private:
+    DEPRECATED_SignalThread* t_;
+
+    RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(EnterExit);
+  };
+
+  void Run();
+  void OnMainThreadDestroyed();
+
+  Thread* main_;
+  Worker worker_;
+  CriticalSection cs_;
+  State state_ RTC_GUARDED_BY(cs_);
+  int refcount_ RTC_GUARDED_BY(cs_);
+  bool destroy_called_ RTC_GUARDED_BY(cs_) = false;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(DEPRECATED_SignalThread);
+};
+
+typedef RTC_DEPRECATED DEPRECATED_SignalThread SignalThread;
+
+///////////////////////////////////////////////////////////////////////////////
+
+}  // namespace rtc
+
+#endif  // RTC_BASE_DEPRECATED_SIGNAL_THREAD_H_
diff --git a/rtc_base/signal_thread_unittest.cc b/rtc_base/deprecated/signal_thread_unittest.cc
similarity index 95%
rename from rtc_base/signal_thread_unittest.cc
rename to rtc_base/deprecated/signal_thread_unittest.cc
index 1476186..c280e97 100644
--- a/rtc_base/signal_thread_unittest.cc
+++ b/rtc_base/deprecated/signal_thread_unittest.cc
@@ -28,9 +28,9 @@
 
 class SignalThreadTest : public ::testing::Test, public sigslot::has_slots<> {
  public:
-  class SlowSignalThread : public SignalThread {
+  class SlowSignalThread : public DEPRECATED_SignalThread {
    public:
-    SlowSignalThread(SignalThreadTest* harness) : harness_(harness) {}
+    explicit SlowSignalThread(SignalThreadTest* harness) : harness_(harness) {}
 
     ~SlowSignalThread() override {
       EXPECT_EQ(harness_->main_thread_, Thread::Current());
@@ -70,7 +70,7 @@
     RTC_DISALLOW_COPY_AND_ASSIGN(SlowSignalThread);
   };
 
-  void OnWorkComplete(rtc::SignalThread* thread) {
+  void OnWorkComplete(rtc::DEPRECATED_SignalThread* thread) {
     SlowSignalThread* t = static_cast<SlowSignalThread*>(thread);
     EXPECT_EQ(t->harness(), this);
     EXPECT_EQ(main_thread_, Thread::Current());
@@ -157,7 +157,7 @@
     rtc::CritScope cs(&crit_);
     return has_run_;
   }
-  void OnWorkDone(SignalThread* /*signal_thread*/) {
+  void OnWorkDone(DEPRECATED_SignalThread* /*signal_thread*/) {
     FAIL() << " This shouldn't get called.";
   }
 
diff --git a/rtc_base/signal_thread.h b/rtc_base/signal_thread.h
index 9229ca1..b444d54 100644
--- a/rtc_base/signal_thread.h
+++ b/rtc_base/signal_thread.h
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
@@ -11,148 +11,9 @@
 #ifndef RTC_BASE_SIGNAL_THREAD_H_
 #define RTC_BASE_SIGNAL_THREAD_H_
 
-#include <string>
-
-#include "rtc_base/checks.h"
-#include "rtc_base/constructor_magic.h"
-#include "rtc_base/critical_section.h"
-#include "rtc_base/message_handler.h"
-#include "rtc_base/third_party/sigslot/sigslot.h"
-#include "rtc_base/thread.h"
-#include "rtc_base/thread_annotations.h"
-
-namespace rtc {
-
-///////////////////////////////////////////////////////////////////////////////
-// SignalThread - Base class for worker threads.  The main thread should call
-//  Start() to begin work, and then follow one of these models:
-//   Normal: Wait for SignalWorkDone, and then call Release to destroy.
-//   Cancellation: Call Release(true), to abort the worker thread.
-//   Fire-and-forget: Call Release(false), which allows the thread to run to
-//    completion, and then self-destruct without further notification.
-//   Periodic tasks: Wait for SignalWorkDone, then eventually call Start()
-//    again to repeat the task. When the instance isn't needed anymore,
-//    call Release. DoWork, OnWorkStart and OnWorkStop are called again,
-//    on a new thread.
-//  The subclass should override DoWork() to perform the background task.  By
-//   periodically calling ContinueWork(), it can check for cancellation.
-//   OnWorkStart and OnWorkDone can be overridden to do pre- or post-work
-//   tasks in the context of the main thread.
-///////////////////////////////////////////////////////////////////////////////
-
-class SignalThread : public sigslot::has_slots<>, protected MessageHandler {
- public:
-  SignalThread();
-
-  // Context: Main Thread.  Call before Start to change the worker's name.
-  bool SetName(const std::string& name, const void* obj);
-
-  // Context: Main Thread.  Call to begin the worker thread.
-  void Start();
-
-  // Context: Main Thread.  If the worker thread is not running, deletes the
-  // object immediately.  Otherwise, asks the worker thread to abort processing,
-  // and schedules the object to be deleted once the worker exits.
-  // SignalWorkDone will not be signalled.  If wait is true, does not return
-  // until the thread is deleted.
-  void Destroy(bool wait);
-
-  // Context: Main Thread.  If the worker thread is complete, deletes the
-  // object immediately.  Otherwise, schedules the object to be deleted once
-  // the worker thread completes.  SignalWorkDone will be signalled.
-  void Release();
-
-  // Context: Main Thread.  Signalled when work is complete.
-  sigslot::signal1<SignalThread*> SignalWorkDone;
-
-  enum { ST_MSG_WORKER_DONE, ST_MSG_FIRST_AVAILABLE };
-
- protected:
-  ~SignalThread() override;
-
-  Thread* worker() { return &worker_; }
-
-  // Context: Main Thread.  Subclass should override to do pre-work setup.
-  virtual void OnWorkStart() {}
-
-  // Context: Worker Thread.  Subclass should override to do work.
-  virtual void DoWork() = 0;
-
-  // Context: Worker Thread.  Subclass should call periodically to
-  // dispatch messages and determine if the thread should terminate.
-  bool ContinueWork();
-
-  // Context: Worker Thread.  Subclass should override when extra work is
-  // needed to abort the worker thread.
-  virtual void OnWorkStop() {}
-
-  // Context: Main Thread.  Subclass should override to do post-work cleanup.
-  virtual void OnWorkDone() {}
-
-  // Context: Any Thread.  If subclass overrides, be sure to call the base
-  // implementation.  Do not use (message_id < ST_MSG_FIRST_AVAILABLE)
-  void OnMessage(Message* msg) override;
-
- private:
-  enum State {
-    kInit,       // Initialized, but not started
-    kRunning,    // Started and doing work
-    kReleasing,  // Same as running, but to be deleted when work is done
-    kComplete,   // Work is done
-    kStopping,   // Work is being interrupted
-  };
-
-  class Worker : public Thread {
-   public:
-    explicit Worker(SignalThread* parent);
-    ~Worker() override;
-    void Run() override;
-    bool IsProcessingMessagesForTesting() override;
-
-   private:
-    SignalThread* parent_;
-
-    RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(Worker);
-  };
-
-  class RTC_SCOPED_LOCKABLE EnterExit {
-   public:
-    explicit EnterExit(SignalThread* t) RTC_EXCLUSIVE_LOCK_FUNCTION(t->cs_)
-        : t_(t) {
-      t_->cs_.Enter();
-      // If refcount_ is zero then the object has already been deleted and we
-      // will be double-deleting it in ~EnterExit()! (shouldn't happen)
-      RTC_DCHECK_NE(0, t_->refcount_);
-      ++t_->refcount_;
-    }
-    ~EnterExit() RTC_UNLOCK_FUNCTION() {
-      bool d = (0 == --t_->refcount_);
-      t_->cs_.Leave();
-      if (d)
-        delete t_;
-    }
-
-   private:
-    SignalThread* t_;
-
-    RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(EnterExit);
-  };
-
-  void Run();
-  void OnMainThreadDestroyed();
-
-  Thread* main_;
-  Worker worker_;
-  CriticalSection cs_;
-  State state_ RTC_GUARDED_BY(cs_);
-  int refcount_ RTC_GUARDED_BY(cs_);
-  bool destroy_called_ RTC_GUARDED_BY(cs_) = false;
-
-  RTC_DISALLOW_COPY_AND_ASSIGN(SignalThread);
-};
-
-///////////////////////////////////////////////////////////////////////////////
-
-}  // namespace rtc
+// The facilities in this file have been deprecated. Please do not use them
+// in new code. New code should use factilities exposed by api/task_queue/
+// instead.
+#include "rtc_base/deprecated/signal_thread.h"
 
 #endif  // RTC_BASE_SIGNAL_THREAD_H_