The 1980's and 1990's happened.
Here in my state of Connecticut in about 1984 as a wee little one, I clearly recall that it was common for pickup trucks to legally have rifles/shotguns on the rear window gunrack. It was also common for a used pickup in the classified ad to have options like: New tires, gunrack, winch, plow.
By about 1986 the option "gunrack" was rarely mentioned because you couldn't use it anyway. Feelgood (to who) legislation hard at work.
Ah yes, that would be me during hunting season back in the 1970's in CT. My shotgun was proudly displayed in my pickup ON SCHOOL GROUNDS, much like everyone else who raced to the woods after school! So happy to be in Virginia where this time honored tradition continues out in the rural counties.
And BTW, where I live, I see them so frequently, racked up with a firearm, that it is commonplace! Yes, my 4X4 '97 F-250 has it's rack filled with an old Montgomery Ward single shot shotgun, that piece, and my diesel tank and dispensing pump, complete my truck as a classic piece of farm equipment!
John