[Lil bastard]

These are called Signal Reminders and they are well known to motorcyclists.

There are several different types from audible reminders to actual signal cancellers.

Here are a few:
http://www.blinkeroff.com/
http://www.ldrider.ca/techpages/turnsignalreminder.htm
http://www.geocities.com/triker1464/turn_signal_reminder.html
http://www.automotiveelectronicaccessories.com/aeapn420.htm
http://www.ridesafer.com/Blinker_Buddy_p/bb505.htm
http://www.cyclegadgets.com/Products/product.asp?Item=SM
http://www.liteminder.com/