I stumbled upon a cache of Arizona Highways scans on the Arizona Memory Project website. It seems that they took the effort to scan most of the Arizona Highways from 1921 through to 2023 (50 pages in total). The Arizona Highways publication started out functionally similar to the California Highway Bulletin and California Highways & Public Works. The earlier volumes are far more highway centric and have more or less evolved into travelog in modern times. The Arizona Department of Transportation publishes Arizona Highways monthly:
https://azmemory.azlibrary.gov/nodes/browse?datefrom=&dateto=&keywords=&orderby=node_title&order=asc&ntids=W10=&filter=eyJudGlkcyI6WyIxMCJdLCJmYWNldCI6e319&a2z=W10=&page=1&viewtype=grid&type=all&digital=0&in=0&access=0&tax=eyJudGlkcyI6W10sInZhbHVlIjpbXX0=&has=W10=&bid=240&meta=W10=&metainc=W10=
The Arizona Memory Project also has a dedicated historic highway images page. In particular I believe this is the first source I've seen AZ 173 shields displayed:
https://azmemory.azlibrary.gov/nodes/view/217952