I too am in favour of new rules to end this. I'd say the rule could be something like: "link dumps are not allowed".
Lately, I see more and more users who only post links to external websites. That's advertising, and thus not allowed, but somehow they don't just all get banned. There's not even any discussion value, as they abandon the topic instantly, after which the sig spammers take over.
It's for marketing purposes, because when they get posted on public forums the search engine crawlers go and visit them and use that in their page rankings (from an anonymous source)...
Yeah a new rule wouldn't be bad but it'd be hard to work out what is link spam and what clearly isn't.
Maybe "any unfamiliar (not from major site) links posted should have relevant quotes from the page copied on that post". And those quotes can be used to decide if the thread would class as spam or not.