the card is placed in a mechanical imprint device along with a carbon-copy receipt, and the merchant then slides a roller across it to imprint the face of the card directly on the receipt
hah.. yes, I am actualy old enough to have paid that way a few times myself when I was younger. I was always taught to ask for the carbons and rip them up in such cases too.
Also had them whip it out at Fry's once when the computers crashed (and the cashier was a complete idiot that had no idea how to fill out the form, add numbers together and compute tax) but thankfully the computers came back just before I simply walked away due to annoyance.
"Everything should be made as simple as possible, but not simpler." -- Albert Einstein