My suggestion is to show all the banned users + the reason that warranted that ban (may it be perm or temp)
If there's no plugin availble, maybe you could do a monthly topic showing who was banned and for what reason (link to dispute if required)
This is just for book keeping reasons. I've bought and sold a few things to now banned users, some of which I can't get a reason to why they were banned (and at risk of accounts/payments getting recovered). I'd kinda like my paranoia to be put to