Isn't just banning the spammers a better solution?

We can also make up a set of general guidelines for signature campaigns like discouraging rules like having minimum x amounts of characters in a post, and encouraging incentives that encourage better quality posts. Encourage fixed rate campaigns over pay per post.

Members of the community should not over stress the earnings component of a post. (Many respectable members of the community does not wear a paid signature.) No posts should be made simply because the person is participating in the campaign but because he wants to post, share his/her views, join the discussion.