Absolutely no crossed-broadswords pin is shown or listed in any of the various books on civil war era US Army-issued and Confederate Army-issued insignia in my relic-reference library. Therefore, in my opinion it is not a civil-war-or-earlier US Army-issue or CS Army-issue insignia.
Additional info:
In the decades before the civil war, the US Army did issue an edged weapon known as a Short-Sword to artillerymen. Its purpose was for close-combat defense if the battery was overrun by the enemy ...but, a Short-Sword is not a Broadsword -- whose blade is much longer than a Short-Sword.
Also, issuance of short-swords to artillerymen was made useless by the late-1840s/50s arrival of multi-shot pistols on the battlefield. When somebody armed with only a sword comes up against an emeny armed with a 6-shot revolver, the sword guy always loses, and quickly. So, the armies quit wasting money on making and issuing a short-sword to soldiers. By the 1860s it had become mostly a "ceremonial usage" piece of equipment. Notably, there are a few exceptions, occurring in the feverish first months of the civil war. That being said, only a very small number of actual short-swords have been excavated from civil war battlefields.
As BigCypressHunter astutely mentioned, the construction of the pin on the back will help to date the crossed-broadswords insignia.
Regimental numbers and Company-letters (as seen on the broadsword-pin) were not included on any US Army-issued insignia until nearly a decade after the end of the civil war. (Yes, Regimental numbers and Company-lettters were issued prior to the 1870s, but they were separate items, not a part of the main insignia's body, as seen on the broadsword-pin.)