The American Sign Museum in Cincinnati, Ohio is the premier collection of antique and vintage signs in the United States, and is the "keeper of the flame" when it comes to the history of sign making in the US.
One of the things that The American Sign Museum provides is informative histories behind sign making techniques and the signs themselves. There is no doubt that at one time or another you have seen a faded ad painted on the side of a building in an old American city. This is an advertising medium that is seldom used now, and as progress and property development continues in these cities, it is an absolute certainty that one day, none of these "ghost signs" will be left.
"very few of these elder
buildings still speak of their colorful histories beyond the Historic
Register plaques with surviving "ghost signs" advertising
long-extinct businesses and products. And as the structures
themselves, these ghost signs rate recognition as true museum pieces
in their own separate category.
Most of us are familiar with the biggest and most grand of these
"frontier phantoms" visible on the Gulch Eddy's, Helena Hardware
Co., and Firestone Tires are old friends with relatively clear
lettering and easy recognition. Same with the Parchen Block's GENERAL
ARTHUR CIGARS. But do we know of all the others, some hidden and some
so faded as to be nothing more than tantalizing fragments" (excerpt from following the linked article) LINK
Frontier Phantoms - Touring Helena's Ghost Signs