This is a GAR (grand army of the republic) button that union veterans would wear post war to reunions. Started in 1866 lasting to 1956 when the last reported civil war veteran died.
Also to add to my last comment, I have a few myself and don't believe yours is a reproduction button. Construction evolution of post war buttons for the most part involved higher domed faces, larger rims, different or blank maker marks, multi piece construction and floating shanks. Those are some things to keep in mind and characteristics your button has. People do make reproduction buttons for sure but the font lettering and color is usually off from originals.
So was it used on military jackets or Fireman jacket or what? Do we know for sure because of the insignia? Just asking, I don't have a clue. All I know is that the buttons came from a shop in Dallas, Texas.