|  | SIGNALLING A LEG BYE |

Umpires signal a leg bye with a hand touching their raised knee and this is done when the ball hits the body of the batsman, but not the bat. The ball does not necessarily have to touch the leg to be called a leg bye.
It can be any part of the body, except the hand holding the bat.
I've not yet fallen over while signalling a leg bye, but there's always time!