Lock the thread; create a self-moderated thread
It's impossible for everyone to start creating self-moderated threads and you can't force people to do it, if they simply don't want to do the moderating job.
You can have many threads like this but this won't change a thing if creator is not active and deleting stuff all the time.
This can have more negative sides with many members avoiding to write in self-moderated topics.
Only shitposters would avoid writing in a self-moderated thread, and I never forced anyone to do so; I only offered a solution that would reduce spam to a bare minimum; isn't that worth a shot?
I would rather emphasize here the responsibility of campaign managers who tolerate this type of spam posting. Most campaigns are run by casinos and gambling sites and it is to be expected that they want their signatures in the gambling section, but various bonuses only encourage additional spam. A lower payment rate will bring the lower quality of signature posters, in the end, less effort from the manager himself to check every post from every participant.
The gambling board is starting to look more and more like the bounties section which is completely moderated by the campaign managers.