An old New York phone exchange on 47th Street

Spotted on an unremarkable building on West 47th Street in the Diamond District: an old-school New York City phone exchange, in this case “MU.”

What does it stand for? Murray Hill, of course, the neighborhood where the real estate company that put up this plaque is based.

It’s getting harder to find these two-letter exchanges, which were replaced by numerals in the early 1960s. But they’re out there—especially in the boroughs outside Manhattan.