There are several here who are only here to build their SEO rankings. It is obvious once you know what you’re looking for, but they seem to have gone unnoticed so far. Allowing them to stay will only lead to more of them joining, leading to more spam, and probably worse kinds of spam eventually as well.
They are what is referred to as “group spammers”, as explained at http://blog.boxedart.com/offbeat/10-types-of-forum-spammers/ (see #9):
“Group Spammers might just be the most difficult to spot. The plan involves creating and establishing several usernames in a community, which may all be set up from the same person, or possibly a small gray hat SEO service or other marking service. Each member of the group will then attempt to increase their post count through shallow participation on existing forum threads. Most of their posts are typically pretty short and lack any real substance.”
It’s too tedious to try and report each one, considering the 60 seconds one must wait between reports - it would take at least an hour, and I’m not that dedicated 
If one of the mods wants to PM me, I could help put together a list of the ones I know are spammers (there are a couple I’m fairly certain of, but not 100% sure).