A brass ONE-PIECE button with a backmark saying "...nson" is most likely a Robinsons' Company button, made from 1812 into the mid-1830s. The company continued in business into the 1850s, but we're talking about the date-range of its 1-piece buttons. The company was known by various iterations of Robinson and partners, such as R&W Robinson, and Robinsons, Jones & Co.