Time-dating:
A brass 1-piece flatbutton with indented lettering in its backmark indicates manucture from "about" 1810 through the 1830s... after which time, flatbuttons fell out of favor with the public due to the advent of mass-production of inexpensive "ornate" machine-stamped 2-piece buttons.
Origin:
It can be either British or American-made. Sometimes a flatbutton's backmark has a national-origin clue, such as British spelling (like "colour") or an American eagle, or a company-name or initials. Can't see any of those on your button.
Value:
Brass 1-piece flatbuttons in the same condition as yours sell for about $1 at civil war relic shows.