Climax Bill Tube

A bill is borrowed and the  owner asked to sign it. The bill is folded, and given to the owner to hold and  wrapped in a hanky. The performer now produces from his pocket a solid brass  tube, which is locked. The performer walks up to the spectator holding the bill,  and whips away the handkerchief. The bill has vanished. The tube is unlocked,  and within it is the same signed bill. A precision machines prop in solid  brass.