help with markings

[ahleeds]

with alot of careful scraping and sanding i uncoverd these bumper markings and one on the hood, red or white square then yellow cicle the numbers on blue/red then number 15 on blue/red . the oldest marks are the yellow circle and number 15 and the hood yellow circle, the rest are on top of many paint layers.
also wondering about the white square on back end tucked way up out of the way?
does this tell us anything about this truck , is there any original pictures out there?
any help would be more than i know now , thanks Anthony