You don’t notice them until you’re looking for them: the tiny cameras perched above the doorways of buildings, focused on the sidewalks below. But surveillance cameras are everywhere — in the subways, behind deli counters, in dressing rooms, outside housing projects and suspended next to every traffic light in the city.

New York City boasts over 10,000 surveillance cameras, some 3,000 of which are operated by the Police Department. Some were installed more than 20 years ago, as a way to fight personal crimes like shoplifting or robbery. But most were installed in the last few years, as part of the city’s growing efforts to fight terrorism.

“These cameras provide a level of passive security, and not only have a deterrent effect on crime, but also record incidents as they happen and serve an evidentiary purpose,” said Robert Castelli, Director of the Criminal Justice Program at Iona College, noting that the closed-circuit camera footage of the London subway bombers entering the tube station last summer allowed authorities to identify the bombers.

But as the number of surveillance cameras in New York has skyrocketed, some people have questioned whether their use is an invasion of privacy.

“There’s a lot that goes on in public that’s nobody’s business,” said Bill Brown, a pro-privacy activist. “People have a right to walk down a street without being watched.”

Despite the objections of privacy groups, efforts are under way to expand their use. Currently, Mayor Bloomberg and New York City Police Commissioner Ray Kelly are considering implementing a so-called "ring of steel" counterterrorism zone around Lower Manhattan. Modeled after a program in use in Central London, the ring of steel would limit public access, increase the police presence and utilize closed-circuit surveillance systems in the area south of Chambers Street.

But amid talk of new counterterrorism tactics on the part of the city, some pro-privacy activists are finding unusual ways to rally public support against hidden surveillance cameras.

Among them is Brown, who leads the Surveillance Camera Players, a 10-year-old group that performs one-act plays in front of cameras, protesting their existence. Originally, the intention was simply to gain the attention of the person watching on the other end of the camera.

“At first it was funny — a group of my friends and I who were against these cameras, would perform in front of them,” said Brown, who co-founded SCP in 1996. “But as time went on, and as the number of cameras increased, what we do has become very serious.”

Brown, who works as a proofreader by day, conducts tours of heavily surveilled areas of New York City every weekend. He guides groups as large as 25 people through Washington Square Park, the Lower East Side and Harlem, pointing out private cameras, NYPD cameras and government cameras.

In addition to attracting New York residents, college students and former law enforcement officials — what Brown refers to as the heart of his attendance — the tours have become something of a tourist attraction. This year, Budget Travel Online began listing the Surveillance Camera Players walking tours as one of its recommended ways to see New York.

But don’t mistake Brown’s tours for a lark. He considers them an opportunity to win over new supporters, who will hopefully return to their own communities and start similar groups. Already, Surveillance Camera Players groups have popped up in Cincinnati, Chicago and cities in Arizona. Moreover, Brown consults with groups around the world, who are fighting the proliferation of cameras in Lithuania, Turkey and the United Kingdom.

The culmination of these efforts was the worldwide days of action against surveillance cameras, on March 19-20, 2006. In New York, Brown’s group led a walking tour of Harlem and conducted a performance in front of a webcam in Times Square. Similar demonstrations took place in Austria, Cincinnati and the United Kingdom

“As I see it, this is a very simple issue: we must choose between privacy and surveillance. We can’t have both,” Brown pointed out. “The question is, what kind of society do we want to live in?”

But Castelli rejects that notion. “The cameras are nothing more than an extra pair of eyes watching down a public street,” Castelli said. “Their potential abuses are outweighed by their gains.”