Originally Posted by CommuterRun
I use hand signals. Right Turn-straight out to the right, Left Turn-straight out to the left, Lane Change-pointing out and down to whichever side I'm changing to. Very big, very visible and very clear signals. Another blinky light on the back of my bike would probably go completely unnoticed.
http://www.bikemiamivalley.org/safety1.htm
These are the only legally accepted and recognized signals I have ever heard of. Using your right arm may not be visible to motorists (as they tend to be on your left).