My opinion a good way to decide if an account is a spammer, is to see if he just literally repeats what someone has already said. They generally don't read what people have typed. albeit, if the thread is 9 pages, sure, but usually its good practice to read the the last page...so many people just keep repeating and repeating what has been said just to earn them campaign coins....
You mean people saying exactly what was just said, instead of reading? Like I just did right now, just to prove your point? 
Another obvious sign is when 9+ out of 10 posters have a paid signature. The campaign I'm in recently stopped counting "the obvious spam threads" that are filled like that.
Quote
I dont see why campaign managers would care? I mean the whole point of campaigns is to get exposure for whatever it is
If the thread is mainly filled with other signature spammers, the exposure it gives the campaign will be worthless.I notice that a lot of threads end up like this, 30 signature farmers all talking to eachother, while everybody else has abandoned that thread, even if the thread did start out useful.
My preferred "solution" now it to use the signature as an indication whether or not the post if worth reading. The bigger the signature, the less likely it's worth my time.
This solution of yours...means that you may miss out on a quality / informative post made by someone who isn't actively participating in a signature campaign or a newbie, like myself.