Regarding the shape of the symbol, I've always been convinced that it was inspired (even if unconsciously) by the US Army Cannon Heater's feed door draft plate:

Regarding the shape of the symbol, I've always been convinced that it was inspired (even if unconsciously) by the US Army Cannon Heater's feed door draft plate: https://picturearchive.gunauction.com/2450084810/12565270/gedc0186.jpg_thumbnail0.jpg https://picturearchive.gunauction.com/2450084810/12565270/ge...