It looks like it says GOODYEAR BEST I. ON . V*Your find is what button-collectors call a 1-piece brass flatbutton. (The shank/loop is not counted as a piece.) That type of button with the backmark written in indented lettering dates from about 1810 to about 1835. I can make out the name "Goo0dyear" in the backmark, a reference to Amasa Goodyear of Waterbury CT... which dates your button to about 1815-21. The company name became Goodyear & Son in 1821-26, then "& Sons" from 1826 until 1835.
The rest of the backmark seems to say "Best" and then something else. If you can read the entire backmark, please tell us what it is. That might change the time-dating a bit.