Card marking is the process of altering
playing cards in a method only apparent to marker or conspirator, such as by bending or adding visible marks to a card. This allows different methods for
card sharps to
cheat or may be used for
magic tricks. To be effective, the distinguishing mark or marks must be visible on the obverse sides of the cards, which are normally uniform. Card marking is often used to cheat when
gambling or for
card tricks. Many casinos, particularly those in
Las Vegas alter the decks of cards they sell to tourists – either by punching holes through the middle of cards or trimming their edges – to prevent cheaters from returning to the game tables after buying the cards and then slipping the favorable cards into their hands when playing.