Systems include an automatic card shuffler and a shoe. The automatic card shuffler may include a printing device for applying a randomly selected set symbol on each card of a set of cards. The shoe may include a set symbol reader for reading each card for a presence and identity of a set symbol. A shoe processor may be configured to receive a signal from a shuffler processor indicating the selected set symbol to enable the shoe processor to verify that each card belongs to the set of cards. An automatic card shuffler includes a processor programmed to randomly select a card set symbol and a card-marking system for forming the randomly selected set symbol on cards. Methods include forming a randomly determined set symbol on each card of a set of cards and detecting whether cards include a set symbol matching the determined set symbol.