Originally Posted by signupdamnit

Maybe it's just me but I consider it incredibly rude to stare at someone paying to the point where I can identify the type of card they are using. That's almost as bad as looking over someone's shoulders to watch them enter their bank pin number. I know there are cultural differences but here in America if I feel someone is too close to me while I enter my bank PIN I won't hesitate to ask them to back off or at least give them a long dirty look.

Unless the card has some big red X or huge writing which says FOOD STAMPS it seems to me that if you can tell you are likely already looking for it and you know what you are looking for. The only way I have ever known that someone in front of me was using them was when either they or the cashier mentioned it and that has been extremely rare.