I would keep it simple. I would just hand it out to #Amethyst users if requested.
Ideally nostr:npub1gcxzte5zlkncx26j68ez60fzkvtkm9e0vrwdcvsjakxf9mu9qewqlfnj5z would bless it as an official #Amethyst badge, that would add validity.
Discussion
I'm not saying this one exactly, but something of the sort or along the lines of the Amethyst logo.