U.S.A. (1940) Flex-O-Glass*. Postal card (O) with advertisement on back for Glass Substitute - Flex-O-Glass. Also Window-Fabric, Glass-O-Net, and Wyr-O-Glass. Fascinating!
AVAILABLE AT $20
U.S.A. (1920) Cartoon caricature of window washing*. Two cent (overprinted 1c) cent (UX32) postal card (O) with illustrated ad on reverse for Sun Window Cleaning.
AVAILABLE AT $20
U.S.A. (1887) Window glass. Natural gas. 1c postal stationery envelope with ad.
AVAILABLE AT $12