Inside the life of a the Nightvale Sheriff’s Secret Police. Get to know them and you’ll find out they are people just like anyone else - slipping in their darts one feather tipped poison needle at a time.
And yes, that’s a skull on their shoulder. Does that mean it’s a human skull? No.
As it turns out, it’s not a human skull at all. Look closely and you’ll see it’s much too small to be a human skull. Too small, and far, far, too old. Why, if it were any kind of skull, it would have to be the skull of a long-dead race of beings that only bear the slightest resemblance to us. So don’t worry about it!