Bill Tube by Bazar de Magia.

A bill of any denomination is borrowed from an audience member and then signed. The magician then folds the bill into a small bundle, places it under a handkerchief and gives everything to the owner of the bill to hold. The magician then displays a locked brass tube which is given to another spectator. They examine the tube and certify that there's no way to open it up without first removing the lock. The handkerchief is then whisked out of the spectator's hand and their bill has completely vanished! The magician gives a small key to the spectator with the tube. They unlock it and inside find the signed bill! Comes with large-capacity, high-quality brass tube (the fitting is invisible), padlock, velvet carrying bag and instructions.