53 Pa. Stat. § 4594
Every registered master plumber shall have a bona fide place of business in said cities, in the case of any borough, incorporated town or township of the first class, either within the said municipality or within a distance of one mile from its nearest boundary, and shall display on the front of his or their place of business a sign, "Registered Plumber," bearing the name or names of the person, firm, or corporation, in letters not less than three inches high.
Signs displayed on buildings not occupied as a bona fide place of business (other than advertisements) of any registered master plumber, firm or corporation, must not be construed to permit or allow said registered master plumber, firm or corporation to establish the same privileges or benefits as registered master plumbers, firms or corporations within the limitations of any city or municipality.
53 P.S. § 4594