It's kind of like how moderators don't delete potential scams. I doubt that they would take action against signature campaigns if they were too troublesome and caused some inconvenience. Most YoBit signature wearers have post qualities that are debatable, but good enough to dodge the ban hammer; and IMHO, YoBit is the campaign with the most spammers.
As for signature campaigns without a manager, he's talking about bots counting the posts. Bit-X, BitMixer, YoBit, and a couple others do it.
EDIT: Plus botany's reference.
If you're going to start banning people for semi constructive posts, many would just think that the forum is limiting free speech. It isn't all about being troublesome. Trusted users can submit a list for moderators but it would have some bias-ness in it. Most signature campaign uses bot for post as there are too many users. However, some signature campaigns limit the max post or the sections. This does help the spam abit. Some signature campaign does frequent checks on the post quality which is quite good.