Snuff with debossed F

This is very nice example of an open pontiled snuff. Very clean, nice olive amber color. Theory is that the F stands for Foster, one of the proprietors of the Stoddard glass works. Seems unlikely to me. Why would he put his F on a common snuff when they had so many other much nicer products. My guess if that the F and W that are found on a few snuffs signifies the company they were made for, or possibly the strength of the snuff.