Not much to "identify" about a brass 1-piece flatbutton. "Backmarked" ones were manufactured by the millions in the latter 1700s through early 1800s for use on civilian coats, jackets, and pants. Probably more than half of the ones dug in America were made in Britain. If the backmark on a brass 1-piece flatbutton is written in raised lettering, it dates from approximately 1790 into the 1830s. If the backmark lettering is indented, as yours is, it dates from approximately 1810 into the 1830s, when this type of button fell out of favor with the public due to the advent of machine-made inexpensively-priced "fancy" 2-piece brass buttons. The use of the term "plated" on brass 1-piece flatbuttons meant silverplate. What we now call goldplating was called "gilt" in flatbutton backmarks.