I was told that if that was once the case, it is the case no longer- really the signature is only to verify that someone was there to have made the purchase, to decrease the store's liability if it is a fraudulent charge.

This is why the charge to the card goes through before you have to sign anything. Even on pos systems where you sign on the screen, I get the text message notifying me that my card was charged even before I start to sign on the screen.