The memo does not allude to its origin, and a department spokeswoman declined to discuss what had precipitated it. The spokeswoman, Inspector Kim Y. Royster, said such memos were “periodically circulated to remind personnel of our policies.” She added that it “comports with the N.Y.S. Court of Appeals ruling on taking enforcement action against individuals for public nudity.”

The memo’s language is as clear as it is legalistic. Officers “shall not enforce any section of law, including penal law sections 245.00 (public lewdness) and 245.01 (exposure of a person) against female individuals who are simply exposing their breasts in public.”

Katherine Rosenfeld, a lawyer at Emery Celli Brinckerhoff & Abady who is also representing Ms. Van Voast, saw a direct connection between the memo and her client’s public performances, often done in the character of a mustachioed “topless paparazzo” called Harvey Van Toast. “It establishes that they’ve been in error in all the times that they’ve charged her,” she said.

Ms. Van Voast, in her lawsuit, is seeking compensation from the city as well as punitive damages from several named and unnamed officers for her treatment, which the suit alleges constituted civil rights violations.

The memo reminds the officers that there are still times when they can detain, arrest or give tickets to women or men for being indecent in public — “if the actions of any individual rise to the level of a lewd act (e.g. masturbation, simulated sexual act), regardless of whether the individual is clothed above their waist,” or if the person is naked below the waist “and is not entertaining or performing in a play, exhibition, show or entertainment.”

Of a dozen patrol officers from precincts around the city interviewed on Wednesday, nearly all correctly cited the law on toplessness, though none would describe roll call discussions. Each declined to be quoted by name, citing departmental policy.