The trick, as Noah pointed out, is extremely similar to Karrel Fox's Karate Card. However, when I first read your post concerning the effect that you were describing, it sounded very much like Tom Mullica's torn and restored (which undoubtedly has roots in Karrel Fox's)however, his version did not contain a signature. The trick, I believe, is published in An Evening at the Tom-Foolery (Kaufman) but to my knowledge, the book may be out of print.
The difference is that a card is selected (no force), and you propose to find it behind your back. Behind your back, you find the card, and bring it out facing yourself, and name the card. You tear the card, give the spectator the top piece, the other pieces vanish in your hands, and when the deck is spread, the selection is seen face-up in the center, with the corner missing, and the corner is matched. As an after-effect, Tom Mullica then tears the selection (the remaining 3/4 of it) and while he's tearing it, the card transforms into the selection, but a fully uncreased, whole card version. It looks amazing. I hope this helps