From a thread on CCKW.org
Postby Kees51 » Tue Nov 07, 2006 2:30 pm
I forgot to look in the obvious place. Exerpts of a manual on vehicle markings are right here on the cckw.org site, in the Bumper Numbers page under the Techical Info tab. There are pages from the AR 850-5 manual of August 6, 1942 and pages of the AR 850-5 manual of February 15, 1945.
The 1942 manual says about the registration markings: "The markings on the vehicle will be with blue-drab lusterless enamel by means of a stencil."
The 1945 manual says about the registration markings: "Registration markings will be applied with approved white lusterless, stenciling, synthetic enamel."
So it seems they ceased to worry about being photographed from the air.
So it seems that at least one other person has found the 45 AR850