History 1942 GMC rear-end

I recently bought a 1942 GMC and I noticed the rear -end had embossed design GMC, can anyone tell me when they could of made them?

 

Nice, if you don't use it, I'd sure cut that whole dome off of there for a wallhanger, or a doorstop or something.

 

I've seen them as late as '54 on bigger trucks. I don't know when they were first used. I like it, send it to me for my shop wall!

 

never seen one, and i've looked at many gmc rears lately......wonder why they're on some and not others?