SWEET. I thought it was a lock escutcheon at first.... but the club shape seemed interesting. I think I'd have a difficult time getting my size 14 foot into whatever boot this fell off of.
That's an interesting story but is unfortunately a myth (I have heard that about the heart pattern in particular, but it is not substantiated anywhere). They were simply heel plates for ladies shoes ca 1860s era (not CW related), they were made in the five card suits at the time (hearts, diamonds, clubs, spades, and stars).
There was another myth that different CW companies wore given suits on their boots, but why would you want to tip off the enemy? It was established that they were used on women's shoes when an intact lady's shoe was finally dug with one from a trash pit. Also note the generally diminutive size of these plates--they are too small for a man's heel.
It's nice to find one intact as many were discarded when they broke.