place them into a group “banned” and set a group flair (whatever icon you want).
beyond that, you could use CSS to add elements to their user card with .primary_group “banned” tag on elements
also, do you happen to know a couple guys we called “the Bobs” (Bob & Robert) that used to run a 10k user smartthings group on facebook?
With that kind/level of moderation and use of the ban hammer, you guys would get along.