What about all the vans and panel trucks that have no side or rear windows at all? You just have to use your mirrors.
If they are legal it seems the stickers should be legal too.
I’m not trying to be a wise guy - just asking.
I'm in an industry where most contractors use these types of American made cargo/work vans. I own two, myself.
I'm around these sorts of vehicles all the time, but I can't remember seeing one such as you describe. They usually have windows on the right rear side, or the rear doors - most often, both.
I could be wrong, but I don't think I've seen one with NO windows on the cargo compartment.