Meaning
A single katakana character, サ (sa), on a square button, short for the Japanese word for service. It indicates a service charge, as printed on menus and bills in Japan.
It fits notes about restaurant fees, hotel surcharges and tips: “Menu prices are before 🈂️, so expect a bit more on the bill” Outside Japan it is mostly used by learners of Japanese or simply for its neat look. Some people read it as a stylised letter S.