US WWII uniform insignia Identification help

[Jeremy T Garner]

A good friend of mine just lost his grandfather and inherited his grandfathers uniform among other belongings. I have helped him ID most everything and have came across something that has me and a few other fellow collectors stumped. I am trying to ID this piece of insignia and its meaning from the jacket. Any help would be greatly appreciated. His Grandfather served in the US Army In the 26th Infantry. I do not recognize this pin and would love to gather whatever info I can for my grieving friend. My guess is it's a distinctive unit insignia (DUI) of some kind???

[psteinmayer]

Never seen that one before... but if I had to guess, I would imagine it has something to do with Armored Cavalry... but again, this is purely speculation.

Pretty awesome though...