Your number (XII) reflects the fact that you're the 12th Sean Foster to register on IMDB.
Emma Stone is listed as Emma Stone (III) as she was the 3rd with that name on the site.
And she's got an IMDB rank of 11.
BTW if you look up names using the IMDB app on your phone, you won't see those numbers. But they're visible on the actual IMDB page.