I know around here, and many places around the US, you can purchase gasoline and just swipe your card, no signature needed. What I learned years ago from my CC rep was that the only legal way to check identity on a CC is to compare the signature on the card with the signature of the person standing in front of you. He even told me it is against VISA/MC rules to look at a seperate ID.
Now, I don't know if rules have changed, but it is obvious that people do a lot of different things. VISA/MC also won't allow anyone to limit the amount of transaction allowed (like, minimum $10 purchase to use CC), but many places do it.
But, my guess is that no signature is either allowed in certain places or certain industries. It may even become common. I don't know what a merchant is allowed or not allowed to do, but I am sure a phone call or two would tell you.