Ok this is a probably silly question and I am blind. If there is an existing banner and I go to make a different topic a banner it will say “There is currently a banner topic.” . The issue is that can’t see a way to find out which topic that is if I have dismissed the banner myself ages ago.
Visit the forum in incognito mode and you’ll see it.
I feel like I should give up my nerd card for not thinking of that. Thanks. 