I purchased this from ebay, but I can't figure out who would have issued it. Any ideas?
I am intrigued by the plumed helm and the crossed halberd on the coat of arms.
The intriguing symbol I say is a "trophaeum" (trophy), a combination of battle spoils, mounted armour, helmet and weapons, that was built by the Greeks and Romans on the sites of battlefields as a symbol and reminder of the victor's triumph.
The trophaeum has been used in various time periods and by various military and paramilitary organisations as a symbol.
Without more information on your short sword itself, I am not able to find out more on age or type, but there are some edged weapons experts in here to help you with that.
Couldn't pinpoint a specific image of a trophaeum matching yours but I hope this info helps you further.