African American students were not so very rare. Did not see any pictures of him, but again, the thing is, you would have known him if you were a) part of the same matriculating class b) ate in the same dining halls c) if he lived in on-campus housing. None of these things applied. Another thing: Obama arrived as a transfer student, so he did not go through the Freshman orientation, wouldn’t have made all the social connections that go along with entering school together with the rest of his classmates.
I’m not trying to argue either way. Just explaining why I would not necessarily have known him and why he might not have been so well known at the time.
One curious footnote: in the years he was supposed to be there, it was the height of the Anti Apartheid movement which was very big on the Columbia campus. Most of the rallies were held right outside a building I worked in frequently as a student manager of a buildings and grounds office. If he was an activist for that cause, I would have remembered him there because the protesters hung around there for days. I do think I remember George Stephanopolous hanging around with that crowd.
You probably weren't that well known either but bet you could round up more than his 3 people who knew you when. Guaranteed that everyone who attended any of his so called schools ran to pull out their memory books and racked their brains to remember if they passed him in the hall.