I just read a terrific article over at Debt Ninja about signatures and credit cards. If you are one of those people who doesn't sign your credit card (and there are far too many of you), you'll be in for a surprise. If you are one of those who just signs "See ID", again, there's a surprise.
I was surprised - and I sign my card - about the actual reasons behind why you have to sign. As a retail worker, nothing pisses me off more than people shoving unsigned credit cards at me and then getting tetchy when I ask for a driver's licence. Apart from the fact that there is no signature to compare on the card, it says right on the card, right on the back, right above/below where your signature should be "CARD NOT VALID UNLESS SIGNED." They mean it, you know.
Anyway, read this. I found it interesting and am glad to know the reasons behind it. And it's not the one you probably think it is.
This is the link for the Creditcards.com article that was the basis for the guest post on Ninja.