Thumbs up
From Floor Pi Wiki
Thumbs up is a hand signal used to indicate approval of anything. It is made by forming a fist and pointing your thumb upwards, accompanied with an enunciated "Thumbs up!".
Variations include using both hands instead of one to indicate even greater approval, "Thumbs down!" to indicate disapproval, and "Thumbs diagonally downward!" to indicate a slight disapproval.