which is why I also point with my fingers. My right turn signal isn't the 90 degree raised forearm with upper arm parallel to the ground that the teach in driver's ed. It's more like the upper arm is pointed slightly upward and the forearm is at a more acute angle, so it looks like I'm in the middle of throwing a high punch to my right; and my fingers are also pointing in the direction of travel to reduce the ambiguity

Seems to work for most of the drivers behind me.

and for folks who poo-poo hand signals because it requires one to take your hands off the handlebar; I mean no disrespect, but honestly, that's more of a deficit in one's bike handling skills than it is a flaw in the system. If you don't signal because too many things are happening and the streets are too chaotic and you can't take more than a second to move your hands off your handlebars then you should slow down, get stable, then signal.