My 2c here.... I don't think the shirt actually points to any job speficially.

Yoshida has said in the past that XIV is going to be going more in the direction of OC jobs rather than jobs that existed in previous titles. As such, there's not really much of a hint that can be given off his shirts to say what it might be if the correct answer is a job none of us have ever seen before, but it's still something players expect. So he wears the ninja turtle shirt as a way of telling us that the new job uses scouting (see also ninja) gear.