I cannot see how someone could be held responsible, if they did not know that the project that they supported in their signature, were a scam.
They can't, and the best scams are the ones which aren't obvious. If someone genuinely believed the project they were promoting was legit, and there was no evidence to suggest otherwise, then I don't think it would be fair to red tag that person (situation dependent).
However, as OP has shown in his screenshot, when a project is discovered to be a scam, usually someone posts in their ANN/bounty/campaign/whatever thread in big red letters stating it is a scam, and giving everyone time to remove their signature or stop posting their bounties. If you heed this warning, you aren't red tagged. If you ignore this warning, you are. I think that's fair.
Agreed. I even think it would be fair to send a warning via PM to that user to warn them of the consequences, if he or she continues to wear that signature. Some people do not regularly visit the campaign page or the ANN thread, so they might not have noticed the warning in those threads.
A PM will also send a email to the member, so he or she will not have an excuse that they missed the PM on the forum or that they have not logged into the forum to read that PM.
