Mexico City's authorities have started handing out 15,000 plastic whistles in the name of combatting sexual harassment, despite widespread ridicule of the idea.

The whistles are supposed to give women in the Mexican capital an option for drawing rapid attention to any harassment they suffer in public places, scare their attackers away, and warn others in the vicinity.

Mayor Miguel Ángel Mancera's announcement of the plan in late May triggered a wave of jibes on social media.

"What will be next, rattles to battle kidnappings and party blowers against corruption?" one Twitter user wrote.

Others joked about the way the whistles' brand name, ACME, evoked the name on the disastrous inventions used by Looney Tunes character Wile E. Coyote.

Women's rights advocates, meanwhile, condemned the plan for putting the burden of protection from harassment on its victims, rather than dealing with institutional weaknesses that mean few report the crime.

The National Institute for Women reported earlier this year that more than 126,000 women suffered some type of harassment in the capital's subway in 2015, but less than half a percent went to the authorities.

Almost 94 percent of sexual crimes go unreported in the country as a whole, according to figures from the CEAV, the government commission responsible for providing attention to victims of all kinds of violence.

Activists have long highlighted the way victims are put off going to the police because they know they risk being criminalized themselves. Many also dread getting sucked into a time consuming judicial process full of endless paperwork that is unlikely to lead to a prosecution, let alone a sentence.

Mayor Mancera, however, was defiant in the face of the scorn prompted by his whistle plan that he insisted was just part of a wider campaign to combat harassment in public places. He stressed it also included reinforcing surveillance on the public transit, designating more women-only wagons and speeding up the process to file a report.

"As with every new project, people will have to become used to the whistle," he said at the time.

Even so, the criticism has appeared to have had an impact. The whistles distributed at subways stations this week are black. The original prototype displayed in May was white and pink.