Originally one point was that you signed the back of your card and the merchant would compare the signature on your receipt to the signature on the card to veri

Originally one point was that you signed the back of your card and the merchant would compare the signature on your receipt to the signature on the card to verify your identity. Another point was so the merchant has proof you intended to pay them. When I was living in the UK (which wisely uses a more sensible PIN system instead of signatures) I was shocked the first time someone asked to see the back of my card. I don't think it's ever happened to me in the US. Culturally we've collectively decided to ignore the whole "signature verification" thing, but when using your card abroad you sometimes are reminded that it's supposed to happen in theory.