TBH, I agree that focusing on the users would be a better idea. I have to admit that there are a couple of quality posters in YoBit/BitMixer; if the campaign itself was closed down because of the spammers, then that would mean that they would be affected as well.
I'm still a fan of using a system more centered on the users, an ignore a specific signature button, which ignores all sigs of that type, and at a certain point they would automatically be ignored for everyone, though this is more complicated to implement.
Not sure if I understand what you mean. Are you saying that the signature itself would be automatically ignored for everyone, regardless of the user showing the signature? IMHO, ignoring a specific user instead of a signature type would be better; we would weed out the spammers, and the people who were making good posts with that signature would continue to get paid.
I like the idea of the ignore color; it sounded like a good idea. Maybe implement that again, but a less CPU-consuming method?