That is a Castigator Sergeant who's had pretty much all of the skin from his face burnt off by a melta-bomb. According to the fluff written up by the Castigator's creators, they commonly wear symbols of the Inquisition in acknowledgment of campaigns in which they have participated for the benefit of the Inquisition.
Actually not. This was done basically because I like the home-brewed chapter that someone on Bolter and Chainsword created... thus I make some various illustrations on the subject just because I like to... one of the best chapters out there, legit or custom.
Hurray! I thought they were another one of those obscure references that people wouldn't necessarily 'get,' but I am always happy to be incorrect. Granted, this one is a lot less obscure than the one with our dying sister of battle.