If negative tags don't solve the problem of people continuing to promote this campaign, is it possible to expect a signature ban for each participant? Is this signature ban also a moderation of scam?
Everyone should be aware of what kind of trust feedback users have even if it's not 100% effective at preventing someone from promoting fraud. It's clear that disallowing campaign participant from using signatures is part of
"regardless of what campaign they promote" fraud moderation so it's very likely that admin will never approve it. Rather than asking admin to ban them from using signature then it's good to report every post of this user for deletion especially if it's spam it's much more appropriate than asking admin to moderate scams like 1xbit campaign.
After that, you can still ask each manager to blacklist them if necessary as this is the most effective way to not let them promote other campaigns after 1xbit campaign.