I think it is not possible for someone to make 30 or 50 posts in an hour.
Why not - you just need to prepare 50 posts in notepad and post them every 15 seconds, 30 seconds, or 1 minute between posts on the thread you want. If you really do it - then I'm sure you can probably post 50 posts in less than 1 hour. Such posting patterns may be rare - but burst posts are always possible among spammers who don't care about quality.
Well, that's a valid concern but I don't think that anyone will prepare 50 posts in notepad and post them every 15 seconds as that really don't make sense at all in real life but yes as a theory you're right it can happen. The participants in signature campaigns will never do something like that and that's somewhat impossible for them. Most of the participants spend time on forum rather than giving time to notepad in order to write those posts altogether.