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I saw this on an answer I downvoted recently when I went to post a comment and I was briefly confused as to where the comment button went. Then I realized I no longer needed to comment because the banner is basically identical to the comment I would have left, minus the last sentence.
How do these banners come about? Is this a site-specific things? What rep do you need to add one? How are they removed? etc.
Basically: explain this site feature to me, please.