To a top flight grandmaster, even a signal indicating "think now" is sufficient. No actual variations or moves need to be communicated. Vishy Anand had mention

To a top flight grandmaster, even a signal indicating "think now" is sufficient. No actual variations or moves need to be communicated. Vishy Anand had mentioned in an interview that he would be virtually unbeatable if he received a simple signal from an observer indicating that the current position is a critical position in the game.