So, I was sitting on the top floor of the double-decker bus on the way to work and reading Prisoner of Azkaban. I read this paragraph and something jumped out at me:
"It's on his case," she replied, pointing at the luggage rack over the man's head, where there was a small, battered case held together with a large quantity of neatly knotted string. The name Professor R. J. Lupin was stamped across one corner in peeling letters.
Lupin has "Professor" stamped on his luggage in letters that are peeling off. So, these are the possibilities I see:
- He taught at another school of magic previously
- He taught at a Muggle school previously
- The case used to belong to a relative, maybe his father, who had the initials RJ
- He's really lousy at name-stamping charms