Tokyo (CNN)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 (about $24), sold out within 30 minutes of going on sale on Tuesday, a company spokesman told CNN.
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.