Even though we gamers never get to see Master Chief's face, he does take off his helmet occasionally in both the books and video games, so it's not a secret what he looks like. But mostly, Master Chief does of course wear his helmet, and especially in battles.
This isn't anything the creators of the Halo TV series could care less about though. In the show, we rarely see our favourite Spartan John-117 with the helmet on, something that really has angered the fans, especially the fact that he doesn't always use it even in battles. This has led to the Halo community photoshopping all posters from the show where we see Pablo Schreiber's face so that he wears a helmet instead.
Perhaps the message has got through, as Paramount has now released two new posters from the seemingly intense second season of the Halo TV series, and this time, the Chief wears his piece of head armour as intended. Check them out below.