and here is the 24x36 US guide sign from 1944.
this sign was to be enclosed in a wooden frame; I omitted that in the drawing. The wooden frame is about 1" wide in pictures I've seen of this style of guide sign, and it's mounted to poles, therefore there are no mounting holes on the sign itself.
the 1944 reference manual does not specify the shield size, so I shrank a slightly later 24" Maryland US shield down to 16x16. The only US route shields mentioned in the manual are 16x16 embossed - perhaps an embossed route shield was to be affixed to the guide sign? Examples are, alas, sadly lacking.
also, the 1944 manual specifies either Stimsonite buttons, or reflective sheeting. This design clearly has the sheeting option.