The 'Banned' avatar should only appear on that person's profile page or in the thread he/she was banned in, or have a mechanic where getting banned deletes all recent posts by that person.
Currently, if I make the nicest post in the world in one thread, commending or congratulating the original poster and then I go get banned for trolling in another thread then everyone who sees my nicest post in the world thinks I got banned for that post and it can be a misleading perspective on moderators.