Of course, you could even have a floating window placing the cursor above the player which displays this information.
I insist on the chat, because it would also be innovative for this section of the game, I have seen it in other games and it works very well.
In my opinion, it wouldn't have to because the moderators' etiquette is very different, but on the other hand, users would be interested in having those ribbons when they see them in the chat.
I think that PvP ribbons go unnoticed and I also think that they could have a similar function to that of vanitys, thanks to displaying them through chat and the overworld.
They could motivate those users to want through their exposure to obtain them.