Installation of Flashing Yellow Arrow (FYA) signals is becoming more common in California and other states.  Drivers are familiar with the typical 3-section left turn signal, with red at the top, yellow (amber) in the middle, and green at the bottom.  The FYA left turn signal is a 4-section head, including the three familiar sections plus an added yellow section that flashes instead of displaying a steady arrow.
 
For a great informational video on how they work, visit http://srcity.org/909/Flashing-Yellow-Left-Turn-Signals