A spectator chooses a card from the deck and initials it on both sides. The remaining cards are placed back into the card box, with the selected card sticking out halfway. There’s no switch involved; it’s genuinely their initialed card. You then write your initials on the card box. In an instant, your initials magically transfer from the box to their initialed card. You promptly hand them the card, along with the card box, which is completely examinable.