The green eyes pierce the night, arresting pedestrians who notice the mute blinking orbs above the bustle of Herald Square in Manhattan. But for the most part, the glowing specters go unnoticed by many.

People stare into their cellphones at a bus stop across the street. Businessmen walking home focus on their routes ahead. A double-decker bus, stopping at a light, alerts riders to what they might otherwise miss, but usually only the most observant New Yorkers stop to ponder the glow.

It comes from the eyes of two stern-looking bronze owls perched atop a tall granite monument in the northern part of the park in Herald Square. They are among New York City’s more obscure architectural oddities. Lighting up every night from dusk until dawn, they can be seen blocks away, their blinks lasting approximately two seconds. But they are not modern additions.

The owls have glowed nightly, barring periodic electrical disruptions, since the monument was completed in 1940, and they were lighting up elsewhere even earlier than that.