You can already report it to the staff via the link and/or report it directly to the campaign manager.
But many people dont know about that, But when they see a link in the signature about report abuse and they are redirected to a link where they can post, i think they will surely do that.
So if they don't know about or click on the report to moderator button why would they click the other one? The admins aren't going to force campaigns to waste space in their signature when there is already a perfectly good button that does the job.
Edit: @Qickseller, Why did you voted No? I thought you are the one at the top of the list who want this, what is your opinion ?
Of course I voted no. The forum has no business regulating what people are saying as long as it is somewhat coherent. By forcing people to have a report signature abuse link on any paid signature the forum would be forcing people to say something.
I think campaigns (and companies that campaigns are advertising) should do a better job of preventing people from posting useless garbage. They should be proactive in preventing people with weak posting histories from joining and when someone that is already in a campaign starts to post weak posts, they should quickly be kicked from the campaign.
This. If campaign managers did their job and either didn't pay or accept poor posters quality would improve dramatically and spam decrease drastically. If shitposters were turned away from every campaign then they would have no choice but to improve their posts.