The California Department of Conservation list the Tsunami Warning Signs as follows:
Very strong ground shaking along the coast is an indication of an earthquake that could cause seafloor displacements and/or a submarine landslide large enough to generate a tsunami. Though many large earthquakes have occurred along the coast without causing a tsunami, you should still be aware of the potential and plan accordingly. In the event you are at the coast and feel strong shaking, it would be prudent to move to higher ground.
In situations where tsunami travel times are short (due to nearby earthquakes or landslides), it is difficult for government agencies to identify and warn the public. Individuals should know what the natural warning signs of a tsunami are and have a plan to evacuate if necessary. One noticeable, but not universal, sign is the rapid receding of ocean water from the beach before the first tsunami wave hits. In many accounts (including the 2004 Indian Ocean tsunami), this effect has caused greater loss of life because it became a curiosity that attracted people to the oceanfront.
In order to determine whether a tsunami has been generated following a large earthquake, scientists from the National Tsunami Warning Center monitor an array of buoys and tide gauges that measure vertical changes to the ocean surface (more info on ocean tides and currents). If a potentially damaging tsunami is headed towards California, a warning will be broadcast through the Emergency Alert System and the National Oceanic and Atmospheric Administration (NOAA), National Weather Service (NWS) Weather Radio (http://www.nws.noaa.gov/nwr/). Check with your local city or county to see what ways they will notify you of a tsunami.