After eating lunch at a local restaurant yesterday, I noticed that when I was signing my receipt they had printed my whole credit card number on there. I hadn’t seen that happen in years, and I immediately scratched it out. I happened to be with a group of cyber security guys, and they were all in disbelief as well.
It would be very easy for a thief to pick up your receipt just after you leave, then go home and have an online shopping spree. The server or anyone else handling your receipt could do the same thing.