This had to be expected. How can they be held responsible for some users posting shit? Did they enroll these users themselves? No, they didn't.
Do you even properly read other input before thinking about your own method again?
Signature campaigns are not started by bots. There is always some user who fires up a signature campaign thread. That user could be deemed as a campaign manager and should be dealt with appropriately...
As far as I know bots only count posts
Mitigation 2: Sign up for campaigns outside of forum. While they keep figuring out ways to mitigate this, we've lost a lot of time and effectively accomplished only minor results.
Could you please reference a campaign which had a sign-up process outside of the forum? Anyway, in this case the service is out of reach while spamming users should be handled on a person-by-person basis