has something to do with the US Government for sure. I can find reference in old maps to U.S.E.D.
Looks like those letters are burned, not stamped. Odd. The USA mark also has no dot after the "A", and the typeface is nothing I'd associate with US-supplied equipment. Those marks also means it was done after the wood was finished
US Department of Education would have been 'DOED"
The US Army Corps of Engineers has a 'Environmental' mission, I wonder if somehow that fits in the 'U.S.E.D.' referenced in the maps. CoE oversaw the Manhattan Project, they did other obscure things too I'm sure
I feel that the "U.S.A" markings are private-owner made marks
I have asked over at the US Militaria forum about U.S.E.D.