DeSoto Building, 1915
This sign has actually improved over the years. Originally advertising Overland automobiles, sometime in its history it had been painted over with "Used Cars" with probably the dealer's name along the top. It's now been restored to the original "Overland." The Overland has not been manufactured since 1926 so this sign has at least an 80 year history.
See this from NW 8th and Davis.