I was trying to figure out his "method," and here is my theory...
He ends every post with some vbulletin-looking image, but they are from an outside source, and not actually from this forum. I think the idea is for the posts to all look harmless, let some time pass, and then swap out the images on the back end to turn them into some sort of spam.
His sig isn't even a sig - it's text he has inserted into every post, manually...
At least that is my theory. I could be wrong, but I don't really care either, so just to be safe, I'm going to BAN him and delete all of his stupid posts.