Actually I got my driver's license in Japan and we were lectured on signs people on mopeds and supposedly on bicycles use when making right or left turns. Apparently, only one hand is used for signaling, I forgot which one. But if you extend it fully you are about to turn to that side, if you extend it bent in the elbow at 90 degrees with hand showing straight up to the sky you are about to turn to the side opposite of the extended hand. Never seen anyone use these in actual traffic. No other signalization was mentioned.
If I put my left hand up to the sky to turn right I doubt anyone would register what I wanted to do. I am more inclined to use the hand signals @theBlob is alluding to after drivers cut me off or get to close.