The thing is, no one understands arm signals any more. I like to do an exagerated, extended, pointing motion with my right arm and hand. My wife disagrees but I see too many cyclists doing a hasty left turn signal with their left arm tight up against their body. Yes it's the correct signal but no one notices it. What ever you do it needs to be clear and exagerated. Arm signals were designed for use by people in cars. You only had your left arm available for signaling. On a bike you have both arms.