Whenever I have rented a box truck in USA, the vehicle height has always been printed on the dash, and usually on or near the driver door on the outside, and sometimes on the back of the truck, too. And as others have said, they make sure they tell you, too, and it’s a big bold point on the contract that height damage isn’t covered by the insurance. You have to be a real idiot to not know the height. Whether you do anything with that information is an altogether different matter.