This would kill the majority of the spam problem here IMO. Prevent it in the user profile, posts, signatures, etc, until they have at least 5 posts. I've seen many other forums do this. There are scripts available for vbulletin that will outright prevent whatever action the user tried to take until they remove the URL from the post or their profile change. That will stop most spam scripts in their tracks.
There are more spam accounts here than the admins realize. If you want an example, have a look at all of the user profiles in the alphabetic sorted members list. Zero posts and they all link to porn sites or domain parking sites.
The forum becomes a more appetizing target for spammers when it can be used to boost their pagerank. Take that ability away and you'll see less spammers trying to come here because it will largely be a waste of time for them.
and to add to that, prevent pictures for the first 10 posts... im getting sick and tired of clicking into a thread at work only to find porn and the likes.