A Japanese-style button with 'reserved' written on it.
Unicode: U+1F22F
The 🈯 emoji depicts a square button or sign with the Japanese word for 'reserved' written on it. It's commonly used to indicate that something is reserved, booked, or unavailable. The design is inspired by traditional Japanese signage.
Don't sit there, that seat is marked with 🈯!
I've booked our dinner reservation, so we have a table with the 🈯 sign.