"No shoes, no shirt, no service" is a sign you see in a lot of US stores. In San Francisco, restaurateurs might soon have to add "no pants" to the list, as a row flares over nudism in the vibrant heart of the city's gay community.

On a sunny September day, Woody Miller strolls through the district, known as Castro. He's tall and fit, with a long grey beard and heavy silver nose ring -- and wearing nothing more than sneakers, a baseball cap and a watch.

"I go naked on a nice day because I like the feel of the sun and the air on my skin," says Miller, 55, who is one of the city's growing number of public nudists, popularly known as Naked Guys.

"There's nothing obscene about the human body," he adds. "The belief that there is is something that's taught. It's just another form of prejudice."

Home to the gay rights movement of the 1960s and 1970s, the Castro -- where sex shops coexist with trendy cafes and bars -- is still one of the most free-thinking neighborhoods in this famously liberal city.

But even the Castro has its limits, says Scott Wiener, a 14-year resident of the neighborhood and its newly elected Democratic member of the San Francisco city council.

He is proposing legislation that would require nudists in San Francisco to cover public benches or seats before sitting down on them, and to cover themselves altogether before entering a restaurant.

Violators would be fined $100 for a first offense, $200 for a second, and $1,000 or more -- plus a year in jail -- a third time around.

The Castro is "ground zero" when it comes to public nudity, and particularly Jane Warner Plaza, an enclosed seating area at the throbbing intersection of Castro and Market streets, the councillor said.

"In the last few years it's become more obnoxious and in your face," he said. They hang out and pick up a lot of the seats there, and sit down without covering. It's unsanitary."

Miller thinks Weiner's initiative is unnecessary.

"Putting something down before you sit down? I think that's common etiquette," he said. "You don't need to legislate that. It's right there in the 'nudist handbook'. You don't go anywhere without your towel."

California state law prohibits exposing one's genitals "with lewd intent" -- but the way the law is applied in San Francisco, so long as no-one is obviously aroused, what?s lewd is in the eye of the beholder.

Members of the public can perform a citizen?s arrest, but police won?t arrest nudists absent a complaint.

Miller's disdain for Weiner's proposal is shared by another Castro nudist, writer and businessman George Davis, 65, who in 2007 ran for mayor on a platform of making clothing optional in Golden Gate Park.

"It's an irrational fear," he said, wearing a hat, sunglasses and a mobile phone on his hip, and referring to worries about nudism and public health. "You ought to be more afraid if I cough on you than sitting where I sat."

Wiener's bill would also ban restaurants from serving naked patrons, an idea that Michael England, a server at Orphan Andy's, a 24-hour diner in the Castro, thought rather redundant.

Orphan Andy's already has a dress code -- typical right across the United States -- that requires diners to wear shirts and shoes, "and pants, too, I suppose."

But Davis pointed out that other restaurants do serve naked diners. "I don't know why they want to burden restaurateurs with a whole other level of bureaucracy," he said. "It just seems to be a little bit micromanaging."

Supporting the bill is James Viggiano, 57, a San Francisco resident and regular visitor to the Castro who recalls going to a few restaurants and seeing clients with nothing on.

"I don't think that's healthy (and) I find that offensive when we've got kids living around here, and we've got tourists, and all of a sudden we're becoming a nudist colony," he said.

But over at the Hot Cookie bakery, owner Dan Glazer thinks the Naked Guys might be a tourist attraction in their own right.

"My intuition is that it helps business," he says. "We have no problem with naked people at Hot Cookie. We sell cookies in the shape of penises."

Wiener says his proposal -- which is waiting to be heard by the San Francisco city council's public safety committee -- won't trample on the right to self-expression.

"Some people view this as an infringement on San Francisco being different and not being mainstream. If I was proposing to ban public nudity, I would understand," he said.

"But sitting uncovered on public seating has nothing to do with being an odd or different neighborhood."

For dedicated nudist Davis, however, there is one thing that will make him cover up: San Francisco's famously unpredictable weather. "The wind is winning," he says, pulling on a pair of trousers.