Did every interviewer give you a business card? If so, it could be an institutional thing.
But if not (really either way), I wouldn't take it as a definite positive sign, but it can't be a bad one, right?
I've gone on a number of interviews and have never gotten anyone's business card. Not that my example necessarily translates to anyone else.
But in any case, I would say that it could be a good sign and at the worst, no sign at all. It's alright to feel good about yourself!