there are half a dozen each night mainly from Indonesia or China that either try anon posts or go through the process of creating an account. 95% make their first post with a link of some kind. Some of them even submit avatars. The smarter ones start with a question which is followed up later with another new user with "the answer" which of course has links, or try some banal posts to "season" the account first before trying for a post with a link.
Nearly all of them are human, not bots. I mean they're human bots if that makes sense, paid to try to squeeze links into forums. Currently there are no automated bots registering and posting, those afflict pre-packaged sites like wordpress etc.
If they're not purely trying to spam SEO links, they're trying to find ways to mention the products that make people a lot of money: video converters, VPNs, facebook tools, etc. Stuff that regular joe thinks a page 1 hit in google or a forum post recommending it is good enough for him to fork over $69.95 for.