From Paul Lukas of Uni Watch comes this extraordinary find: The demolition of some buildings on the south side of Flatbush Avenue between 5th Avenue and Pacific Street reveals this ancient painted ad for a framing concern. I make it out to be approximately 1880 or so. Amazing stuff and thanks Paul for being Johnny on the spot. If anyone has further details, leave a message in Comments.
In Comments: Henry O’Neill Picture Framing at 587 5th Avenue per Lain’s Business Directory from 1885 [weird because the house numbers on 5th Avenue here are 1 to 10]