New traffic signs are popping up across New York, calling out those who like to catcall women, a problem activists say can no longer be laughed off.

They look like real traffic signs and read "No Catcalling Any Time" and "No Catcall Zone." They've appeared in Times Square, near the Barclays Center in Brooklyn and in almost 50 other locations.

The signs are the work of New York-based clothing company Feminist Apparel, which began putting them up last weekend, saying it wanted to raise awareness of street harassment. Activists say that ranges from catcalls and whistles to unwelcome sexual gestures, being followed and even assault.

"It's been normalized for so long," said Debjani Roy of Hollaback, a non-profit network of activists working to end street harassment around the world. "We've been told to ignore it by people who've experienced it before, so for a long time it hasn't been stated as a problem."

A new survey found only three per cent of U.S. women under 40 reported finding street harassment flattering. (Feminist Apparel)

A new survey by Hollaback and Cornell University says 77 per cent of American women respondents under 40 reported being followed by a man or group of men in a way that made them feel unsafe in the past year.

It also found 85 per cent of U.S. women surveyed said they experienced street harassment before the age of 17. The study was conducted in 42 sites around the world, with more than 16,000 women responding, 5,000 of those in the U.S. Results from Canada are expected to be released next month.

"It's about calling it a problem, calling it a form of gender-based violence," Roy said. "It's about reading people's stories about the harassment they've experienced."

The issue of street harassment made international headlines last October when a group posted a YouTube video of what it's like to be a woman walking down New York streets for 10 hours. To date, the video has had more than 39 million views.

T-shirts funded

On Friday, some signs had been taken down by city workers, while others remained. Photos of the signs were being posted on social media with the hashtag #catsagainstcatcalls.

Feminist Apparel funded the campaign through the sale of T-shirts on its website. Similar signs have appeared in Philadelphia as well, in collaboration with Pussy Division, a feminist group based there.

Roy welcomes the "No Catcall Zone" signs as a way to get the conversation going, not just amongst women but with men who, she says, sometimes don't understand the harm that behaviour can have.

"It creates a sense of fear, anxiety and shame", Roy said.

"We have girls as young as seven sharing their stories on our site. It starts really young, and it really shapes an individual's sense of self and their self-esteem."