Enclosed CJK Letters and Months

Enclosed CJK Letters and Months is a Unicode block containing circled and parenthesized Katakana, Hangul, and CJK ideographs. Also included in the block are miscellaneous glyphs that would more likely fit in CJK Compatibility or Enclosed Alphanumerics: a few unit abbreviations, circled numbers from 21 to 50, and circled multiples of 10 from 10 to 80 enclosed in black squares (representing speed limit signs).

Source: Wikipedia — Enclosed CJK Letters and Months (CC BY-SA 4.0)