A spectator freely selects a card from a completely normal (even borrowed) pack and signs their name across the face to eliminate the possibility of duplicates. The spectator's selection is then returned to the pack. The magician sets the deck down and displays two cards from a different deck, which are freely shown then placed on top of the deck face-up.
He snaps his fingers and with absolutely no moves or funny business whatsoever, spreads the face-up cards. Sandwiched in between is one face-down card! When the spread is turned over, the sandwiched card is seen to be the spectator's signed selection !