A new device aimed at tackling sexual harassment on crowded trains and public transport has sold out just half an hour after it went on sale in Japan.
The "anti-groping" stamps, manufactured by stamp-maker Shachihata Inc., allow victims of harassment to mark their assailants with invisible ink, and also provide a deterrent to would-be attackers.
A limited run of 500 stamps, which retailed at 2,500 yen, sold out within 30 minutes of going on sale on Tuesday, a company spokesman told CNN.
When used the stamp leaves the mark of an open palm which can only be seen under ultraviolet light.
The mark is not visible under sunlight, making it very discreet in public, and is quick to use as there is no lid.
A light which is included with the stamp can be used to reveal the 9-millimeter stamp and the mark can be washed off.
Buyers of the product also get a strap which can be attached to bags and show to others that they have the stamp on them.
In May, Shachihata said it would develop the stamp after discussions erupted on social networking sites about how to discourage groping -- known as "chikan" -- on crowded trains.
One social media user suggested pricking the offender's hands with a safety pin, while others pointed out that this could be a crime in itself.
Others suggested stamps could be used to mark and shame offenders. Shachihata, a well-known stamp maker in Japan, hinted it might be able to help to develop the product, and after three months the company revealed trial sales for its first model.
In May this year a video appeared of a pair of Japanese schoolgirls chasing down a suspected groper on a station platform.
Video taken from the platform of Akabane Station in Tokyo showed the man dodging commuters as he made an attempt to flee before another man trips him up.
In a test-run sale, the stamps sold out within 30 minutes, Shachihata Inc. spokesman Fumihiro Mukai told CNN.
"I was so surprised how quickly they were sold out," he said.
Shachihata Inc told customers on Twitter they would post on their website if any more were made.
A spokesman for the company told the Japan Times that after the trial sale, the company plans to adapt the product based on feedback.
Although police have not been involved in the development of the stamp, Mukai told CNN that the company is hopeful that it will help curb sexual harassment.
In a series of posts made on the company's Twitter account Shachihata said the stamp was just a "small step".
They said: "The most ideal would be a world free of sexual crimes. This is a small step. We will continue to think of ways to contribute to society."
Yayoi Matsunaga, head of the Osaka-based Chikan Yokushi Katsudo Center (Groping Prevention Activities Center), said the move was 'very meaningful.'
The release of an anti-groping product "should have a big impact on society, which could lead to deterrence," she added.
Japan is ranked 110th out of 149 countries in the World Economic Forum's index measuring gender equality.
A 2001 survey found two thirds of female high school students in Tokyo had been groped on trains.
The country also ranks bottom among G7 countries for gender equality, despite Prime Minister Shinzo Abe's pledge to empower working women through a policy called "womenomics."