From the creative mind of Shin Lim: THE SWITCH is the cleanest way to switch a folded card for a spectators signed card. 

Imagine placing a Mystery card on a table, in someone's hand, in a clear box, well... anywhere. This is done in full view of the audience. You then have a another spectator select a random card and sign it. On your command you cause their sign car to vanish completely from the deck. The spectator is asked to open her hands, the mystery card that the spectators has been holding the entire time is opened. It is the signed selection! 

THE SWITCH is the cleanest way to switch a card because there are no boxes, no envelopes, etc. Words cannot describe how clean the switch actually is.
You have to see it to believe it...