Alcan Highway Vehicle

[Snowy]

Looking at it magified and inverted and mucking with the luminosity settings, it looks like ??RA POOL
Which could refer to the PRA, the Public Roads Administration. In summer 1943 at the peak of construction the army had over 3000 vehicles at work on the highway, and the Public Roads Administration and private contractors had as many more. Well that's according to my Alcan Highway book ('Highway to Alaska' by Herbert Lanks) this is one of a dozen references to the PRA in the book's index.
But that's just a wild assumption, who knows.