This is a photograph of a postcard. The sign on the postcard is of one of the large highway signs that were found at the summits of ridges on the major highway routes of the 30s thru 50s. Most if not all of these have long ago fallen by the wayside; many have been replaced by less iconic signs noting the elevation and summit name.
This one was located on the “Roosevelt Highway” – today’s U.S. Route 6 at the summit of Denton Hill in Potter County. Although these signs were not of cast iron, they were indeed “Keystone Markers”.