system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do the backs of credit cards say "Not Valid Unless Signed," yet I have never been turned away when using my unsigned credit cards?
gpt
It's supposed to be an extra security measure against identity theft. The merchant can compare your signature on the back of the card to the signature you give when you purchase. You used to do it on a hard copy but now they have the digital signatures, which make pretty much everyone's hand writing look terrible. 

Most retail places have some sort of policy where the employees are supposed to verify the signature. They just don't put effort into enforcing them and the cashier/sales person/ect. probably doesn't care enough to check.