It could be some kind of automated joining script, they sometimes use message boards in this way just to get a website link (usually porn or pills) in the member list. I don't think you get to add a website till after you joined here so that doesn't work, but a bot wouldn't know that.

Anyway it might just be ordinary people, some of them will be for sure so I can't just delete them. If it gets out of hand we'll have to add a human interaction question in the sign up.