Mystery Brass Button - D&B Short #1 

Howdy Folks, as many of you know we are underway with our renovation of the 1820 Brick Farm House. While restoring an exterior window sill, I discovered a brass button embedded in the 200 year old old-growth timber. I need your help to figure out the origin of the 'button'. Is it a button? A uniform item from the U.S. Civil War? I have no idea - so I am hoping that someone out there will know!