The first possibility is that the roof of this tenement was visited by the world’s most boring graffiti artist, who left the world’s most boring graffito on the old chimney.
The second possibility is that a tenant was spray-painting something and used the chimney as a prop. The paint marks are overspray in that case. The problem is that the marks are awfully neat for overspray, and the world’s most careful spray-painter is only slightly more likely than the world’s most boring graffiti artist.
The third possibility is that a surveyor was up there and made this mark to indicate a specific elevation above grade. The white paint is there to provide visual contrast for the red line. Given the size of the building, I’d guess that mark is right around 50 feet up. But that raises the question of why? And that’s an answer I’ll never know.
