REUTERS/Jessica Rinaldi

Thursday evening, thousands of people marched across the Brooklyn Bridge from Manhattan to Brooklyn as part of New York City’s arm of the #Occupy protests. As the masses made their way from the streets of lower Manhattan onto the pedestrian walkways of the bridge (a route I know well from my days of yore bumbling around NYC), a “Bat Signal” appeared on the massive Verizon building at 375 Pearl Street. A series of projections on the iconic building ensued, beginning with the “99%” symbol and progressing through a call to arms/poem of sorts as the protestors traversed the bridge.

So how does one go about projecting word-shaped beams of light onto skyscrapers in a way that can be read by thousands in the area, captured on video for millions more to see, and, y’know, portable enough to cart in and out of … an apartment rented for a few hours?

Xeni Jardin from BoingBoing talked to the man behind the Signal, Mark Read, and got some answers:

Who would have a 12K lumen projector, a big expensive piece of equipment, the most powerful projector you can get?

I knew I wanted to throw it on the Verizon Building. Everyone who lives in New York has looked at that big monolithic structure. For some of us, every time we look at it we think of how cool it would be as a projection surface.

I knew we’d need a powerful projector. But if you had something that expensive on loan for free, you couldn’t just sneak it up on some roof and be in jeopardy.

I knew I had to find someone who lived in a building nearby.

The story of the Bat Signal is a fascinating read from both tech-geeky and socio-political perspectives, and it involves both state-of-the-art hardware and the time-honored combo of gaffer’s tape and a broomstick, to boot. I won’t spoil Xeni’s tireless reporting other than to say there’s nothing like a loaned projector, some cool VJ software, and a city housing resident fond of saying things like, “let’s do this,” when you want stage a massive public projection, guerilla-style.

Check out the Boing Boing interview for the full story.