Meaning
The kanji 無 on a square button, meaning nothing or none in Japanese. On signs it means free of charge, with no fee required.
It suits free samples, free entry and anything that costs nothing: “Refills 🈚, drink as much tea as you like” Fans of Zen and minimalism also like the character for its idea of emptiness. Its opposite is 🈶, and 🆓 says the same thing in English.