panel paintings... on this early of a vehicle... that's interesting for 1921. But look at the length of that tool box! I don't think I've seen any of the wood rim era cars with a full running board length tool box

California Automobile Association Truck posed reading 'We are signing the Victory Highway, San Francisco to N.Y.' 

The side of the White 3/4 ton truck is painted with a view of SF Bay

So, this was part of the AAA roadside sign campaign

https://forums.aaca.org/topic/341211-period-images-to-relieve-some-of-the-stress/page/430/