Hmm... click clack sounds like a Captain Beefheart track.
Anyway, I remember seeing a transaction on a train, where the man coming round taking bookings for dinner did not have a click clack machine. He had a bunch of slips that had already been impressed with the companies info. When he wanted to impress the customers info, he used an individual portion of jam! He placed the slip over the credit card and rubbed the jam pot over it to take the impression. What a wonderful use of technology.