What are some signals in pro wrestling ex lightly slapping the other person while in a headlock?

Even if a particular hold (like a headlock) is legal, it can become potentially dangerous or deadly by accident. While the person in the headlock might be waiting for their opportunity to escape or reverse the hold, they might have to let the other wrestler know if it is excessively cutting off blood flow to the brain, or air supply. Not that the other wrestler will relax the grip, but it is a natural reflex to tap when you are in hold that could cause unconsciousness.