Rule #63 / Point in the direction you’re turning.

Signal a left turn by pointing your left arm to the left. To signal a right turn, simply point with your right arm to the right. This one is, presumably, mostly for Americans: that right-turn signal that Americans are taught to make with your left arm elbow-out and your forearm pointing upwards was developed for motor-vehicles prior to the invention of the electric turn signal since it was rather difficult to reach from the driver-side all the way out the passenger-side window to signal a right turn. On a bicycle, however, we don’t have this limitation and it is actually quite easy to point your right arm in the direction you are turning. The American right-turn signal just makes you look like you’re waving “hello” to traffic.