I run a popular sporting forum using myBB.  Since reaching the first page of the Google results for competitive keyphrases, I get lots of sign-ups from individuals who register and make one post advertising their site. 

I think that if I were able to prevent links in posts and signatures until, say, 10 good posts were made, this would deter these spammers.  Is there a way to do this in myBB, or is a plug-in available for this task?

If not, how do you guys tackle this problem on myBB?

Its actually possible to do this . url bb code will not work for unvalidated members, and there is even one that forces you to register before you even see any content.

How would you go about doing this?