It is an emblem from an early-1900s automobile radiator-cap. Specifically, it is from the Monogram line of "automatic locking radiator caps." The company offered to equip the cap with whatever letter or design you preferred. See the advertisement below. I'll include a photo of one on the actual radiator cap, and another photo showing some of the letter variations which have been found.
For anybody here who didn't already know:
Although these objects have been sold on Ebay (and at some relic-shops) as a "civil war Confederate saddle-shield," the advertisement and photos of them on the radiator-cap are rock-solid proof that these shield-emblems are absolutely NOT a civil war relic.