A nice relic from the mechanical era, it makes a pleasant "CLICK-BUZZZZ-CLACK" sound as the signals change. I found it controling a quiet residential intersection near my home.
Nice find. This is indeed a Marbelite cabinet, however, it actually houses the company's model M-30 electro-mechanical signal controller, not the model M-20. In general, the city of New York uses Marbelite M-30 electro-mechanical signal controllers. Aside from that, General Traffic Equipment and some Eagle E/M signal controllers are also used there.