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.
There is already tough competition for slots in any decent signature campaign on the forum. If you clean up yours, the shit posters won't be able to join anywhere else here, at least, in such amounts. You are trying to lay your own fault (and that of other negligent campaign managers) at the moderators' door. As I have already said it, banning users exclusively for shit posting would be an exercise in both futility and hilarity since they would just register again and then "continue fill forum with spam". In any case, kicking a few campaign managers to do what they should seems to be the most efficient way to get rid of spam...
Barring total and indiscriminate signature removal, of course