That would be George S. Twitchell from Philadelphia about 1856 to 1859. There are at least 3 or 4 different stoneware bottles with his name on them. C. Whittemore was in business a bit earlier, about 1852 to 1855. A lot of the ones you see have a faint stamp that is hard to read but yours looks pretty good. Looks like it is in good shape. I have never found a stoneware bottle at a flea market, if I did I would go all the time. stonebottle