They (we) also had a 3-piece lapel brass; the "U.S." being one piece, a round "background" with a square hole to lock it from spinning, and the "screw-on piece" that screwed onto the US piece.
They also had different colored rings that surrounded the background brass... signifying what outfit you were with. Baby blue was Infantry. Mine was Red for Engineers. Can't remember the others. When you reach 60, after doing time in a forgotten war, "oldtimer's" seeps in. We also wore scarves & right-arm braids that matched the color of the brass coronas.
That one you found is the US & background molded together, right? Those were the "quickies" you could buy in the PX when you needed polished brass in a hurry... or if you were simply lazy.