Since you provided a nice image of some of the Philadelphia Yellow Trading Stamp Company's stamps, I thought I would add a few comments. The company was founded in 1904 and lasted to 1968. It was run by the Lit Bros. Department Store. Stamps were distributed in Philadelphia and surrounding towns.They had many designs for their stamps over the years. The earliest ones were square with the same design as above. I would guess that the ones you show come from circa 1910.1904 was the peak in interest in trading stamps. More than 100 companies had already been formed by then. Most were short-lived. The earliest stamps date to 1891.