The weather was cold, and the protesters relatively few. But among the two dozen or so men who braved the whipping winds for a recent rally near the mayor's home on the Upper East Side, one man's sign stood out.

Robert Lesko at a rally this month on the Upper East Side. His sign read: “Straight Guy Protesting the NYPD’s False Arrests of LGBTG People.” (Yana Paskova for The New York Times) "Straight Guy Protesting the NYPD's False Arrests of LGBTG People," read the message, a comment on a spate of arrests by vice squad officers of gay men on charges of soliciting for sex in video stores. The sign was in the hands of Robert Lesko, who wore a bright red jacket. He shrugged when asked his reason for being there.

"It's a good way to spend a day," said Mr. Lesko, his page-boy haircut obscured by a black cap. "There's another protest at 3 in Union Square." He added: "I believe it's every New Yorker's duty to stand up for the rights of others."

When he's not working, there's a good chance that Mr. Lesko, 48, will be standing up for some cause. While not alone in perpetual protest, he is certainly among the more ubiquitous activists at Manhattan rallies. Each week, Mr. Lesko scours NYProtest, a listing of street demonstrations distributed by e-mail by a fellow activist, and chooses three or four that match his leftist political leanings.

He is known on the scene as a colorful character who often wears costumes that attract news photographers. Several years ago, to protest the presence of Coca Cola products on the New York University campus, where he is a secretary in the George H. Heyman Jr. Center for Philanthropy and Fundraising, Mr. Lesko wore a Coke-can costume that he had made; he also dressed as a barrel of crude oil in 2004 to protest the invasion of Iraq. Other get-ups include Patrick Henry (for a Patriots Against the Patriot Act demonstration in 2004) and a life-size latte (to protest Starbucks in 2005 - "They tell me it appeared in a newspaper in China," he said).

"You have to figure out what will work," he said at another rally a week after the vice squad protest. "Today I couldn't think of anything."

This was last Saturday, and the event was a march in the East Village to protest the proposed elimination of the M8 bus line. He attended this event in street clothes.

"This is Saint Bobby right here," said Michael O'Neil, a media manager for Reverend Billy, a comic preacher who organized the march. "He's a pillar of our community because he shows up. Bobby is the epitome of the community citizen."

Activism came relatively late to Mr. Lesko. He was a child when the Vietnam War was at its apex, though he remembers taking an interest in the covert bombing of Cambodia. The Tompkins Square riot in 1988 failed to incite his inner activist, even though he said he was roughed up by the police after getting dragged into the melee near his Alphabet City apartment. He was once a marketing and advertising major at N.Y.U. - "the worst! Convincing people to buy things they don't need!" he says now - but eventually came to blame a propaganda-laden media for anesthetizing him into complacency. He claims it took years to break that spell.

But it was broken in 1995, he said, after he met an artist at a Lower East Side bar who turned him on to Noam Chomsky and gave Mr. Lesko "The Chomsky Reader."

"In the 10 hours it took to read that," he said, "my worldview changed."

Shortly thereafter, Mr. Lesko signed on as a steward of his union, the American Federation of Teachers - he is now vice president of the N.Y.U. affiliate - and joined a group in support of the Zapatistas, an armed revolutionary group based in Mexico. His involvement soon spanned 40 groups, including the American Civil Liberties Union and Greenpeace, to which he offers support in the form of donations and mailings. Mr. Lesko has taken up the mantle of recruitment, but never in a pushy way, he says. Mostly he sits in bars and waits for people to start conversations with him.

Last week's march to save the M8 was part of a busy couple of days: on Friday, Mr. Lesko was at the Malaysian Consulate at 11 a.m., followed by a much-publicized sit-in at N.Y.U. at 3 p.m., then a protest at 5 over a cartoon printed by The New York Post. Saturday, by comparison, was merely a double-header: After the M8 march, he attended another vice squad protest in Sheridan Square.

For such a dedicated protester, Mr. Lesko is generally shy, "especially when it comes to political stuff. I'm terrified I'm going to say the wrong thing." Perhaps his introverted nature is what safeguards him against arrest, which he is careful to avoid. He takes vacation days only for the really important demonstrations. He lives in a rent-controlled apartment at Avenue B and Third Street, for which he pays $600 a month. He has been there for two decades.

Though the frequency at which Mr. Lesko protests may set him apart from his activist peers, he is quick to draw attention to the "tens of thousands" of activists in the city who toil in obscurity, writing newsletters that often go unread. "Those are the real heroes," he said. "I don't want to extend the impression that the out-front protest work is more glamorous than the grunt work."

An older man approached Mr. Lesko as he stood next to the giant black cube at Astor Place. "What's going on here?" the man asked. After Mr. Lesko calmly explained the proposed M8 cutbacks, the man concluded, "It's good to protest, but you're not going to do anything."

After the man walked away, Mr. Lesko said: "That's what I would have argued for the first 35 years of my life." He added, "You see immediate results from some rallies because they work toward a clear goal, but sometimes I go to protests where I know I won't see progress for 200 years."

Not that progress can be measured one rally at a time. "I want to retire so I can do this every day," he said. "I want to dedicate all my days to this stuff."