Originally Posted by bostontrevor
Many states permit the use of right arm extended to indicate a right turn. It's more readily understood and the only reason left-arm-up was established was because hand signals were initially developed for automobiles and it's real hard for a driver in the US to get their right arm out the passenger window.
The left arm hand signals are what I was taught. It makes sense, from the drivers perspective, to use the left arm, and seems like a better choice for reasons of visibility for the cyclist to use the left arm signals. The city that I live in recommends left arm out straight for a left turn, right arm out straight for a right turn.