Yes, we had a long discussion about updating the rules some months ago, Bssage came up with most of it, and I personally went about updating the actual rules sticky.
http://www.parentingforums.org/showthread.php?t=13613
"1. No Advertising/Spamming:
No posting or PMing to advertise products, services, blogs, other websites, affiliate or referral links. Small, appropriate advertisements are now being allowed in signatures. Moderators have the right to decide if a signature ad is not appropriate, and will notify you via PM if yours needs to be changed or removed. You can also put a url in the Home Page field of your profile. Work at home parents have the option of advertising home-based businesses and the like in the "WAHP links" section."
So essentially, yes, links are allowed in signatures and mods are allowed to decide if they should be removed for any reason. Obviously no one is required to click on these links, and if they are found to be "bad" in any way, they will be forced to remove. As for the garbage pointless posts being thrown everywhere, that is a personal judgment thing that the mods have to take into consideration as to whether or not this person is just trying to spam. If that is decided, mods have the right to take action if desired. Deleting, warning, banning, so on.
Unfortunately we don't catch it all, and there will always be those "loop holes" that people will try to take advantage of, to where they are not technically breaking any rules, but they are still being obnoxious or getting away with undesirable forum behavior. As members, your options to help prevent this from happening or get it taken care of are to report the posts along with your reasoning ie "I think they are posting nonsense just to spam us with their signature link" etc. And mods will go from there as to what to do. We will try to keep that kind of junk cleaned up if we can.
If I notice an ongoing, recurrent problem based around the signature links, then I may consider revising the rules again to exclude them. We will keep our eyes on it.