A spectators signed card changes places with a blank card around your neck.
You show a blank card that is attached on a lanyard around your neck. You ask a spectator to choose and sign any random playing card. The spectator then placed their signed card in a card box. You state that you will make their sign card vanish. When you open the card box there is still a card inside. You explain that their card did vanish and show that the card is now blank. You then remind the spectator that at the beginning you showed them a blank card attached to the lanyard around your neck. When you turn this over, it is now the spectators signed card. Everything is examinable.
Supply your own deck.
"I saw this performed; I haven't been fooled that bad for a long time!" - Kevin Schaller
" Simon showed me this more than 4 years ago now.. Ever since then I have performed this at least once a week and it never ever fails to get a gasp. Such a strong piece of magic that im sure you will never leave home with out.. I never do" - Alan Rorinson