How do you signal a turn?
There are two schools of thought on this. One is the canonical form with a right turn signaled by the left arm extended and the forearm pointing up. The more modern method of signaling has the cyclist pointing in the direction she intends to go.
The benefit of the second system is immediately apparent - it is unambiguous to both cars around and the cyclist who has to remember what signal to make when.
I just came to realize that the signals were developed for old fashioned cars (Model Ts and the like) which weren't as reliable as our cars. If your lights broke in an old car you'd have to use the old-fashioned right turn signal, as the modern one could not be seen.
Now that I understand the reason for the system it all makes more sense, I'm more comfortable in the world, and I'll continue to use the modern hand signals.
Graphic from the Frankenmuth Police Department.