I`m thinking, signature campaigns are not the cause of spam problem. You could post hundreds of posts every day and still be on topic, not spamming, not copypasting. It all comes down to the culture of communacation and reason why somebody came here. If a guy just came on forum to get money he woldn`t care much about rules and content of his posts. He`ll just want to formally get a minimal number that he needs for having his stake/points whatever you name it, and nobody can control amount of posts, coming from all people, whether they participating in campaigns or trying to rank up. Forbid all bounties and signature campaigns, destroy every opportunity to make money out of posting - and this will get you a result of much less spam