Yeah, it’s Voyager. You can long-press on a username to add a user tag. And if you come across the same account later, editing the tag will give you a button to jump to the comment you originally used to tag them.

It also automatically tracks votes, so that [-6] is my running vote total for this user. So I tend to downvote them pretty often compared to upvotes. It makes spotting trolls/idiots a lot easier.

Lastly, (though it isn’t marked here) it will add a baby emoji to any accounts that are new. That one is nice because you often find brand new accounts posting really divisive shit, and they’re obvious troll/astroturf accounts once you realize they’re freshly made.