one tactic that seems to work is to keep a cleaner handy and every time someone does it you interrupt everything to make a point of cleaning where they just touched while looking at them sarcastically like 'wtf you moron' that usually gets the point across without them loosing a digit.
If it keeps up, verbal comments work, and then depending on the environment a smack to the top of the hand catches their attention too.
If it keeps up, verbal comments work, and then depending on the environment a smack to the top of the hand catches their attention too.