Driving south on the FDR, about fifty yards after the exit for the Triboro Bridge, you can see a little green street-name sign, like the kind used at the intersection of two local roads. The sign pointing in the direction you are heading says "FDR Drive," while the orthogonal sign says "Triboro." But you've passed the exit, and can't possibly take a right for the Triboro without scaling several metal railings each a couple of feet high.
In my old neighborhood in Brooklyn, if you head south on Columbia St. between Kane and DeGraw you will pass a sign for a cross-street called Butler. But where the sign is located, the east side of Columbia is a solid wall of brownstones. The west side is bordered by a page-link fence, beyond which are rows and rows of containers unloaded from the ships that dock in the nearby East River. What's more, the sign for Butler St. is fairly new, while its obvious that the brownstones and shipping yard have been there for quite some time.