Just how bad is the problem of groping on public transportation in Japan? A new device meant as a deterrent sold out in a trial run of 500 in just 30 minutes, reports CNN. The device allows women to leave a mark of sorts on gropers—the idea is that they stamp the groper's hand with ink, leaving the symbol of a palm. But it's meant more as a deterrent than a real penalty: The ink is visible only under ultraviolet light, and it washes off as well. The stamps from maker Shachihata come with a black light that illuminates the marking, notes the Japan Times. "I was so surprised how quickly they were sold out," a company rep says. In the past, female-only cars and surveillance cameras have also been used to cut down on the widespread problem, reports CNET.
The $24 product—first suggested on Twitter following a viral tweet in which a doctor suggested victims poke gropers with a safety pin—is a "small step" toward achieving a society free from sexual crimes, Shachihata says. The head of Japan's Chikan Yokushi Katsudo Center (Groping Prevention Activities Center) says the move is "very meaningful" but it's too early to tell if it will prevent sexual harassment. But CNET describes possibilities for misuse—"What's to stop someone from stamping someone to get revenge after being jilted?"—while highlighting a similar product: the app, DigiPolice, which loudly broadcasts the words "Stop it!" on command. (Read more groping stories.)