What do you guys think of a feature that would let the OP of a topic specify some "banner" text that would appear at the top and bottom of every page of that thread (maybe in a colored box, or something)?
Like this one?

The idea is not bad. It will help Campaign managers or the thread creators to write something important like an announcement/news header. But, Whoever never read replies before they apply in a thread won't read that either.
See this, for example. The Campaign Manager said;
If you are prominent Sr., Hero or Legendary Member feel free to apply. You do not need to have earned 500 merit in the last 120 days but please look within and be honest with yourselves about your standing in this forum and the content you produce.
Now Look at the application of a potential participant and what he wrote;
~Hi, I saw in the title that the campaign is open but I'm not sure for which slot, I'm posting my application just in case, thanks!
He wants to participate in a campaign but did not bother to check the thread if any spots are available for him. This is how people ignore most of warnings! People were talking about giving warnings on a page, and look what theymos said;
Honestly, I think that someone that naïve can't be protected. Even if every inch of the page had been full of warnings, he still might've fallen for it,