I use the standard American left hand method which "most" people seem to understand here in the USA.
Back when I rode a motorcycle I used hand signals once in a while, just to attempt to make myself clearer. I was turning into my neighborhood on a left and had my hand sticking out straight left, BOTH oncoming lanes (4 lane street) came to a halt, I was baffled for a moment then I realized they thought I was telling them to STOP. Perhaps I looked like a cop with a full helmet, jacket and a black bike. I wen ton ahead and saw the column of cars proceed after I turned in the rear view.