I've seen many doubles players who before serving, put their hand behind their back. I figured out a year ago that they do this to tell their partner what they're going to do or where theyre going to go. For example, the pointer can mean that I'm serving low, so stay front and back or two can mean I'm serving high so lets do sides. Does anyone have a certain strategy they use this for? It'll be nice to have a strategy with my partner. Thank you!