A Bill is borrowed, and the owner asked to make a note of the number, and sign it, if he so desires.
The Bill is folded, and given to the owner to hold, wrapped in a Hanky. 
The performer now produces from his pocket a solid Brass Tube, which is locked. The Keys for the lock are handed over to a spectator, (or if you like, they could be handed over prior to your borrowing the note), and the Tube is also handed over, or placed prominently on display.
The performer walks up to the spectator holding the Bill, and whips away the Handkerchief. The Bill has vanished. The spectator holding the Keys is asked to unlock and open the Tube. The spectator finds a Bill within the Tube. He is asked to pull it out, and hand it over directly to the spectator who loaned you the Bill. He finds it is the same Bill and can confirm this by his signature, and the serial numbers.
A careful examination of the Bill Tube will not reveal the ingenious working.
The prop can also be used for other effects besides the one above. For example, the penetration of a silk through a solid examined brass tube.