Across Detroit, fleeting symbols of the past hide in plain sight, behind weeds and under veneers of paint. Demolishing a vacant building among empty storefronts on the west side uncovered the telltale gold and green of a Vernors Ginger Ale sign, preserved almost as vibrantly as the artist intended. In faded red, white and blue, Mac-O-Lac Paint makes an expired pitch to passersby on Gratiot near Eastern Market. On the east side, Mohawk Rock and Rye...