Baseball uses hand signals to represent fastballs, change-ups, strikes, outs and "safe." Hand signals are primarily used by catchers to communicate the pitches expected of a pitcher or by umpires to communicate a call.
While each catcher and pitcher tandem have unique signals, the common signal for a fastball is extending one finger downward. Extending two fingers usually signals a curveball, while three fingers represent a slider. A catcher calls for a change-up pitch by either extending four fingers or wiggling all his fingers. Some catchers use two similar signals to also communicate the expected location of the pitch.
An umpire calls a strike by either clenching a fist or pointing a finger to the side. An umpire announces a pitch count by holding up the number of balls with his left hand and the number of strikes with his right hand. An umpire calling a player out does so by performing a punching motion. If the player is safe, the umpire confirms this by extending both arms parallel to the ground and moving them in a crossing motion over each other. The umpire usually accompanies the hand signal with a verbalization; an example is an umpire shouting "Safe" while performing the appropriate hand signal.