A sign is a hand signal used to indicate a desired play in baseball. Signs are often exchanged between pitchers and catchers to indicate which pitches should be thrown and if a pitch is refused, it is said to be "shaken off." Signs are also used in the field for plays such as hit-and-run.

"Stealing signs" is the practice of attempting to learn which signs are being used by the other team in order to gain an advantage.

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