When a question is closed by a user with gold tag badge, this fact is explicitly noted in the database. E.g., for this question the PostHistory table has
and this information makes it possible to render the closure banner with an informative notice about the single-handed closure: Users with the [list] gold badge can single-handedly mark [list] questions as duplicates.
Moderators also have a binding closevote, but it's not recorded in the database in a similar way. The diamonds appearing to their name in closure banner only reflect the current moderator status. This means that as moderators change and their moderatorship period is forgotten, the sites fill with unexplained single-handed closure banners, like this one:
I propose to record the use of moderator's binding vote, e.g., as
and render the closure banner accordingly: e.g., greyed-out diamond with tooltip User had a binding close vote, being a moderator at the time.
If changing SEDE schema is too much hassle, at least give some clue to past mod status in the banner, using the internal isBinding flag.