I bumped into this Model 3 today, with some very odd sensor or antenna attached to back of the roof, driver's side. A dark round rod, a couple of inches thick and about a foot tall, with a bit of an edge around the top. My first thought was that it could be some sort of municipal vehicle (Los Angeles) measuring air quality. But it is very odd that the car did not have any markings or special plates and, most importantly, that it had a custom matte silver paint job. Kind of fancy for a car just doing that. Any thoughts? Perhaps it is doing some autopilot testing? You could see some bulkyish equipment on the back seat through the rear window. The part seemed pretty firmly attached and there were no cables visible anywhere, unlike some other cars that I have seen carrying testing equipment. Or maybe it is an aftermarket accessory that I am not aware of for... I don't know... vaping?