Another idea which could work, something like merging the SMAS list into the trust system:

• On every profile, besides Trust, there's an option to mark user as spammer
• This instantly makes that user's signature invisible for the user who marked him, or add him into the ignore list, to be decided
• If the user who marked him is on DT1 or DT2; staff; or any other list to be decided, then the marked user losses the right to wear a signature. This way, it's not up to signature managers to allow them into a campaign or not. The forum would disable the signature for him

Some details should be discussed, but that would be the idea.