Having been a waitress for many years long ago, we waitresses ALWAYS say "Behind you" if we are coming up behind someone. Seemed to be pretty universal no matter what restaurant I worked in. It avoids food-carrying collisions between people carrying trays and rushing around kitchens and table aisles.

I think few pedestrian understand "On your left".....when people say it behind me whil biking all I usually hear is "____ _____ LEFT!". No wonder pedestrians tend to jump left when you holler it behind them.
I just shout our "Good morning!" or "Passing you!" or "Behind you!". Sometimes Heads up is a good one too. People who don't bike seem to recognize these phrases better than "on your left".