Help Mark badge; badge indicating a hidden disability or medical condition
A badge worn to discreetly signal that the wearer may need assistance due to a non-visible condition, such as an internal disorder, pregnancy, or hearing impairment. Primarily used in Japan.
wasei-eigo (Japanese-coined English), from help mark
If you see someone wearing a Help Mark badge on the train, please offer them your seat.
ヘルプマークは、外見では分からない病気や障害があることを周囲に知らせるためのものです。
The Help Mark badge is for letting others know that you have an illness or disability that isn't visible.