I'm going to take a guess. I think the backmark is for Thomas & James Fassitt of Philadelphia. They were prominent business men in the 1820's. Back in the early 19th C, the letters I and J were sort of interchangeable. That's why we have no "J" Street in Washington DC.
Thomas & James were among the original investors in the Pennsylvania, Maryland, and Delaware Steam Navigation Company in 1826.
Matt - Fantastic! That nails it for me!! Fassitt's were the largest dry goods merchants in Philadelphia at the turn of the 19th C. The button was found in an area that has produced several late 1700's and early 1800's coins - I found an 1830 half-dime in the same hole with the button. Thanks for the super ID