Almost without any privacy concerns. When I went to college around the turn of the millennium, I worked at the main food court on campus. We had a card system just like you’re describing. When we swiped the student’s card to pay for their meal, their student ID would come up on my screen. Their student ID was their SSN. Back then the first three digits of a person’s SSN was based on the state they lived in when they got their number assigned. For most people that was when they were a baby or at least very young, and for most people that’s the state they did most of their growing up in. I used to have most of the codes memorized, so when I’d swipe someone’s card and see that they had an SSN from someplace that wasn’t I’d mention it. “Oh, hey, you’re from Ohio? My aunt lives in Ohio.”