I'm sorry for the late answer, just returned from vacations.
We are definitely going to clean up our signature campaign very soon. May be hilariousandco help us in this work.

I think the problem should be resolved at the level of forum's admins, not sig campaign managers. They could ban users who spam on the forum.
Because our banned spammer may register on other sig campaign and continue fill forum with spam, then try another campaign, etc. But if he was banned on the forum, he can't.