LegendsAll done with the left hand (in the US) with a flat palm and fingers.
Right turn: Extend arm to the side with your hand upward 90°.
Left Turn: Extend arm to the side with your hand outward.
Stop: Extend arm to the side with your hand downward 90°.
Note, any of the above hand motions can be modified with only the middle finger extended instead of a flat palm. This will result in many road goers giving you a honk back as a form of "thank you" for the additional effort in communicating your directional intentions. They may try to have a conversation as they drive by, but as we all know, it's difficult to talk with a helmet on.