Recently, I found this when I was editing: What does the gold circle in the shape of a badge mean? Gold Badges don't appear on all marked as duplicate post notices.
It is a tag badge. There is a silver, gold and bronze tag badge. You get one for each tag depending on the score you earn on each. For example. a gold osx badge shows this gold badge symbol when marking as duplicate. It gives the user elevated privileges to better handle tag moderation.