For Mohan Singh, the breaking point came last year when his granddaughter, who was 6 at the time, saw a seductive woman in an advertisement affixed to the roof of his taxicab. She proudly announced that she suddenly knew what she wanted to be when she grew up.

“The car was parked in my driveway, and the advertisement was there for FlashDancers,” said Mr. Singh, 56, whose taxi has had rooftop advertisements since the day he began driving, five years ago. “And my granddaughter said, ‘I want to be a FlashDancer.’ ”

Disgusted, Mr. Singh recalled how his taxicab, while parked in front of his South Ozone Park, Queens, home, had elicited a similar response from an 8-year-old nephew — only the boy had proclaimed his desire to become a client of FlashDancers — a Manhattan strip club.

Until Thursday, Mr. Singh and other owner-drivers of cabs whose medallions they do not own could do nothing but feel self-conscious and shake their fists at the rooftop advertisements they objected to for ethical, religious or other reasons.