The magician displays a pack of cards and spreads the deck showing that all of the cards have a hole through one end. A spectator selects a card, signs it and returns it to the deck. The performer wraps the deck with two rubber bands, locking all the cards in. Clearly it would be impossible to remove any card from the deck without taking away the rubber bands, so thats exactly what the performer does. However, removing the second band the spectators signed card is seen to be linked to it! The only way to separate it would be to tear the card or break the rubber band!