Advertising sign for F Hills and Sons of Stockton

An advertising sign for F Hills and Sons of Stockton which has just come into the Museums collections. Does anyone know about the Stormproof windows and is the reference to gas tight a wartime precaution against the possibility poison gas bombs? The sign is made of enamelled steel sheet and measures 63.5 x 47 cms. This form of sign dates back to the Victorian era and was once a very common form of advertising and made in a huge variety of sizes and shapes.