Horstmann, the company on the label, was a prominent military haberdasher based in Philadelphia from the mid-19th century to the mid-20th century. It looks like that coat is dated 1913.

That said, it is not U.S. military. The buttons are the state seal of Pennsylvania. Usually, National Guard uniforms followed the design of the regular Army. I would be willing to bet it was a uniform for some state agency or something along the lines of that. More pictures of the full coat would be helpful.