Thought I'd drop these here too, I did happen to notice a couple of Historic US 80 signs in Arizona on the section between Ligurta and Mowhawk Pass in Yuma County when I was on it back in March.
GSV image 1
GSV image 2
There may be more signs than this but frankly I couldn't tell you exactly where they all were.
There's an eastbound shield in Ligurta at
Dome Valley Road. There's a westbound shield at
Avenue 52 1/2 E at Mohawk Pass.
