What are the natural warning signs for a tsunami?

U.S. Tsunami Warning Center FAQs:

"1. Severe ground shaking from local earthquakes may cause tsunamis.

2. As a tsunami approaches shorelines, water may recede from the coast, exposing the ocean floor, reefs and fish.

3. Abnormal ocean activity, a wall of water, and an approaching tsunami create a loud "roaring" sound similar to that of a train or jet aircraft.

If you experience any of these phenomena, don't wait for official evacuation orders. Immediately leave low-lying coastal areas and move to higher ground."

Learn More:

• Surviving a Tsunami—Lessons from Chile, Hawaii, and Japan (Circular), U.S. Geological Survey
  Discusses natural warning signs and other lessons learned from people who survived a tsunami caused by the largest recorded earthquake - a magnitude 9.5 off the coast of Chile in 1960.  The circular is based on interviews with people in Chile, Hawaii, and Japan who lived through the tsunami. 
   
• Ready.gov: Tsunamis (Website), FEMA
  Preparedness information and important facts about tsunamis.
   
• Pacific Tsunami Warning Center (Website), National Weather Service
  Website providing live information on current and recent tsunami warnings.