I had measured our C and posted on the dash it's height.
One morning we came to a very large border crossing into Canada, with several lanes for cars and a few for trucks. Only one lane for cars was open and none for trucks. While waiting for a couple of cars ahead of us we saw a maximum hight sign, we were just a tiny bit too tall. So when it came our turn to move up for inspection, we just sat there and I slouched down and patted the top of my head, I knew better than to get out of the cab without being told to.
The guard came out of his booth and walked up to us and said, I think you can make it. I told him we would try if he wanted but I had it posted here that we were too tall. H said I'll meet you over there at that truck lane.