Initial Here by Gary Jones

https://www.youtube.com/watch?v=MZw9mt_GveQ
An 'Ink Matrix' effect by Gary Jones.

Your spectator selects and signs a card and guards it under their hand on the table. You show three blank cards, each bearing your initials. One by one, your initials vanish leaving just three blank cards. The spectator lifts their hand to discover that all three sets of your initials have congregated onto the spectators signed card.

It's hard to understate the commercial value of this super-easy, offbeat card effect.