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.