Meaning
The kanji 指 on a square button, meaning finger or to point in Japanese. As a sign it marks a reserved or designated seat, as on trains and in theatres.
It is handy for saying a spot is taken or booked: “Front row seats 🈯 for the birthday girl” Friends also use it to call dibs on something. Since the character itself means finger, Japanese learners like it as a vocabulary flashcard.