浴室のドアには鍵がありませんので、使用する際はドアの札を、「入浴中」にして下さい。
There’s no lock on the bathroom (shower room)door. So when you use the room, leave the “occupied入浴中” side of the tag out.
※Tag is like this ↓ 聼起來自然嗎?

You don't have to mention that the room has a shower instead of a bath. Americans ignore that distinction.

There's no lock on the bathroom door. So when you use the room, please leave the "occupied" side of the tag facing out.