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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.
LOL - of course, I wouldn't say it's a make sense to do but that's something that occurred to me about how someone would make burst post up to 50 post in 1 hour.
I would actually say it's crazy if someone ever did it - but it's always possible to create a natural posting rate of 50 - 100 posts per week if they spend more time on forum than in the real world.