Pathos closed hoods with masks
Character-creation hoods also work, there’s a handful of pretty “thief-looking” masks for some races (especially charrs and humans), however I think about the thief as one of the few classes that got quite an amount of armor mixes available, as a thief could also be a chinese-styled assassin, a gunslinger, a sneaky adventurer and so on, but you actually can’t complain about the hoods because there actually are some, I mean look at the engineers…
One thing that I enjoyed doing when leveling was bugging the transmutation. You keep the anonymity hood on you, and have like a mask you dropped. You then transmute the hood looks onto the better stats straight from the hero panel (without taking it off), if all goes well you should now be wearing both pieces and it looks epic! It’s not persistant though…