53 Pa. Stat. § 16564
It shall be lawful for the mayor of the city of Philadelphia to grant licenses under the official seal of said city, to any person or persons desirous to sell gunpowder or gun cotton therein. The person or persons so licensed may have on their premises a quantity of gunpowder or gun cotton, not exceeding in all twenty-five pounds at any one time. The person or persons so licensed shall not be protected against any of the penalties or consequences hereinafter provided for violations of this act, except while they have, on some conspicuous part of the front of each of the houses or buildings in which they may be licensed to sell gunpowder or gun cotton under this act, a sign, on which shall be distinctly painted, in letters legible to persons passing such houses or buildings, the words, "licensed to sell gunpowder," or "licensed to sell gun cotton," and shall pay into the city treasury the sum of five dollars for said license.
53 P.S. § 16564