They are, indeed, spam. And that person has been removed. Honestly I don't quite understand the purpose of them either. In some cases they'll have spam URLs in their signatures or something, even in hidden text. But most of these do not. I've heard that it may be the case that they're trying to appear non-spammy (with no external links), but then they plan to come back after nobody notices anymore, and add in URLs to their signature, and then suddenly all their posts would have the spam URL. Sneaky if so. But we don't let them stick around long enough to do that, if that's the case.
- Oshyan