Car zit
Someone really needs to take better care of their car. Just look at the size of that zip on the roof! There’s no way a zit could grow that big if the car owner just gave the car a wash once every six weeks or so. Obviously, it’s not a zit, but it’s not obvious what it actually is.
It’s not a fish bowl that you place on top of your car, either. There’s a ride-sharing app called Bubbl that caters specifically to passengers with special needs. The bubble on top of the car lets other people know that the driver works for Bubbl.