@Phrenological is right.
As a cashier, the amount of time I spent looking either the back of your card or signature is quantified as being, "as little as possible" (AKA, not at goddamn all for purchases under $500.)
Why? It's not my job. What am I, a handwriting expert? I was never told to do it, and the fact is that none of our agreements with the PCI required us to. In fact, if we see "SEE ID" we're actually allowed by our agreement with the PCI to decline the card in lieu of a signature, as is USPS policy. I never did, because of the Y-Principle: Why bother? Meanwhile, if there is a signature on the card, (including a signature that a thief slapped on there after "SEE ID") we're required to accept it and CANNOT require ID, again, per our agreement with the PCI. Something customers never understood was that we have an agreement with the credit card company, and you have a completely separate agreement with them. We don't have any kind of agreement with you.
Sorry for the long rant, but it was always irritating to have a customer say, "You didn't ask for my ID." I'm not supposed to, and anyone who does is technically violating the card company agreement on behalf of the store. Of course, I've asked for ID precisely once: From a customer who didn't have it on them and got pissed when I refused to swipe their card. After that my manager filled me in and told me, "He's the asshole here, but don't ask people for ID anymore."