Jeeps at Ft. Lewis, Washington, 1941
Private Kirkland drives Col. Thomas M. Monroe, commanding, 15th Infantry.
Notice the rectangle with the diagonal lines? I believe this is unit disignator. I haven’t really found anything definitive in this regard…so it’s still just a guess but other pictures in the set sport different “squares”.
Also notice the rectangle above the square. 15 HQ 13.
Picture Sources: Ft Lewis Sentinel, 1941