An easy way to find your spectator's signed card with just three cards from any deck of cards.
Two aces are pulled from a deck of cards and are placed face up on the table. The spectator picks and signs a card from the deck. You shuffle the signed card back into the deck. Then have the spectator sign the back of the card that is on the top of the shuffled deck. You take the two aces that have been sitting on the table and place the signed top card between the two aces. The top card is not the originally signed card but with the wave of a hand the card is transformed to the spectator's originally signed card.