devtrackers.gg
That's Ice Unicorn which is given to players who match 343 during Community Playdate events.
It's definitely a relatively rare sight to see, but the actual dev emblems are the 343 logo with a halo ring in the background. It's a lot more clear and distinct from the usual emblems.
fun fact that's not the only one 👀
Oh yeah isn't there Fronk?
there's actually a couple that are for the studio but i suspect majority rock the 343 one. :)