B-Sandwiched by Peter Eggink

Effect: The magician displays tow jokers and places them on the table. Next, a spectator is asked to select a card and to sign it across the face. The card is then returned to the deck. The Jokers are picked up from the table, and one card is trapped between them-but it is the wrong card. Magically and visually, the wrong card changes into the spectator's signed selection! Of course the spectator may keep their card as a souvenir.

This effect will hit them like the proverbial freight train! Strong, simple, and visual magic.