NAGOYA--A stamping device that supposedly leaves a humiliating identification mark on the grubby paws of train gropers quickly sold out in a trial online sale on Aug. 27.

Nagoya-based Shachihata Inc., known for its easy-to-use name stamps, said all 500 available “chikan” (groper) stamps were sold in the early afternoon, despite the product still being in its development phase.

The stamp, with a diameter of 9 millimeters, costs 2,500 yen ($23.60), excluding tax.

When applied to the skin of a groper, the stamp leaves a circular mark showing a palm. The stamp can be quickly used in crowded trains and other places because it doesn’t have a lid or cover.

However, the company took into account the possibility of false accusations or nefarious usage concerning the stamp.

The mark is colorless and cannot be seen in natural light. The victim would have to shine a black light, which comes with the device, on the groper’s skin to show others that he can’t keep his hands to himself.

The ink can also be washed off.

The company said it plans to listen to the opinions of users to improve the device.

Shachihata said it would be better if such a device was not needed, but the problem of groping on trains has continued in Japan.

In May, the company decided to make the chikan stamp after seeing comments on Twitter about the groping scourge.

That month, a woman tweeted: “I was advised to jab a groper with a safety pin.”

A flood of replies for and against that measure followed. Some said that drawing blood could work as a deterrent, while others said it was “too extreme.”

Shachihata paid particular attention to a suggestion that an anti-groper stamp be developed.

“We will take countermeasures (against chikan) as soon as possible,” the company said on its official Twitter account. “This is serious and not a joke.”