A cardboard shoe-box (only the box, no shoes needed) and a deck of cards are borrowed. Everything can be examined and the mentalist does not touch anything at anytime. The two objects are handed to a spectator who is asked to shuffle the deck, to choose any card and, without looking at it or showing it to anybody, to put her signature on the back and lay it face down in the box (meanwhile the performer can be outside the room).
The lid is put back on the box (and can be wrapped lengthwise with two strips of adhesive tape if you like) and the deck put out of view.
The performer returns, approaches the box, takes it and, having touched it lightly for a few seconds, names the card inside. The shoe-box is open and the astonished audience sees the signed card is exactly what the mentalist just named.