This 空 character means empty and available in Japanese. This is used in the context of an empty parking space or a vacant hotel room.
CJK Ideographs are characters used in Chinese, Japanese and Korean languages. Their writing systems all completely or partly use Chinese characters.
Japanese “Vacancy” Button was approved as part of Unicode 6.0 in 2010 under the name “Squared CJK Unified Ideograph-7a7a” and added to Emoji 1.0 in 2015.
U+1F233
? Squared cjk unified ideograph-7a7a