Not so, with this physics professor...if he didn't recognize you, you would have to repeat the course (& attend!). On one occasion, a student handed his card to be signed. The professor looked at the name, then at the student, and said, "I've never seen you in my class," and handed back the card.
Now being a science student, he naturally thought quickly, and proceeded to the end of the line. When he was at the front again, he handed his card to the prof. The prof looked at the name, then at the student, and said, "You look familiar. OK," and signed the card.