SAN FRANCISCO — Perhaps it should not be a surprise that San Francisco does not have a law against being naked in public, nor that a small, unselfconscious segment of the city’s residents regularly exercise that right.

That tiny minority was joined this weekend in the autumn fog and cold by unclothed sympathizers at a “Nude-In.” One of their objectives was to draw attention to a proposed law — introduced by Scott Wiener, a city supervisor — that would prohibit nudity in restaurants and require unclad people to put a towel or other material down before sitting bare-bottomed on benches or other public seats.

Mr. Wiener said the law was introduced in response to an increase in nakedness in parks, streets and restaurants.

“It used to be that there would be one nude guy wandering around the neighborhood and no one thought twice about it,” said Mr. Wiener, who represents the city’s Castro district. “Now it’s a regular thing and much more obnoxious. We have guys sitting down naked in public without the common decency to put something down underneath them.”