As I’ve said previously in these pages, you can find all sorts of stuff under elevated trains. Here on an el pillar at Broadway and Rutledge Street, there’s a mid-century triangle sign for the Triborough Bridge that hints that if you turn left, you’ll wind up there eventually.
However, the stub of Johnson Avenue that the sign seems to be encouraging you to turn left on is actually a one-way in the wrong direction.
The next left is Union Avenue and to get to the Triboro, now officially the Robert F. Kennedy, you’d probably wind up taking a left on Union Avenue, then a right on Meeker Avenue, take the on-ramp to the Brooklyn-Queens Expressway and follow that to the westbound Grand Central Parkway in Astoria, which will put you on the Triboro.
But when this sign was probably put there in the 1940s or 50s, the BQE hadn’t been built there yet, and in that case, I wouldn’t know what to tell you!
There’s also a pedestrian control with a placebo button, but they’re pretty common.