Bob, in your opinion, what are the hallmarks of great Chicago-style thin pizza?
Oh boy, that can tend to get a little subjective Craig....depending on which side of the city or which 'burb you grew up in. Everyone has a preference on the (thickness) and amount of crunch to their thin crust pizza. Cooked in a cutter pan or straight on a stone deck, etc.
But as for hallmarks, I guess I would have to say sauce and cheese. Sauce consistencies will vary a bit but is generally something on the thicker side. It is the spices(and good amounts of it too)that say "this is Chicago pizza". Dried herbs such as basil, oregano,tyme,even sometimes ground fennel along with powdered garlic, onion(sometimes fresh that has been put in a blender), sugar, salt, lots of pepper....you'll see any number of combinations of all these. Heavy salt, pepper, onion powder and oregano does it for me.
And then, of course, there is the cheese. Low moisture mozz for the GBD and small burnt "crunchies". Cheese has changed a lot over the years. Used to be much saltier and more buttery. I've recently been adding scarmorza to the mozz and this is delicious. Asiago, provo, Fontina all work as well.
Now for me, Chicago pizza just is not Chicago pizza without some good, greasy fennel pork sausage on it...but now I'm getting subjective.

Hope what I have described above helps.
Bob