The symbol over my health bar and over the heads of other players confused me a bunch as a new player.
The only reference I managed to Google up was a Sep ‘18 post explaining it was your and other players’ levels, but no further elaboration on what exactly each symbol meant.
So I sat and observed my own levels (main and alts) like a hawk over the course of leveling up. Hopefully, this helps clarify some of the confusion for others:
There are also apparently special player glyphs at levels 100 & 150, but one is not quite there yet. I assume it looks more like the Boundless fist symbol.
Vets, please feel free to add images of the high level stuff.