Japanese Language Stack Exchange is a question and answer site for students, teachers, and linguists wanting to discuss the finer points of the Japanese language. It only takes a minute to sign up.
Sign up to join this community
Today I've learnt that in Unicode there's a separate block for katakana letters enclosed in a circle - all of them, apart from ン. Then I've realised that the logo of this particular stack is a letter in circle as well 
My question would be: What is the actual usage of such symbols which is that important that encircled kanas are introduced to Unicode and why nevertheless, an ン is not a thing.
There's a similar question about kanji however it does not cover katakana.
Just like other symbols in this answer, these encircled katakana are mainly used to prefix items in a list. For some reason, Japanese people historically used to like encircled characters, just as English speakers like to use letters enclosed in parentheses ((I), (a), etc). Japanese letterpress companies had many movable types for encircled characters. That said, very few people use these encircled characters today, partially because of the longstanding encoding compatibility issues explained in the linked answer.
ン was not included in the character set probably because ン is a special sound that never comes at the beginning of a Japanese word. It's unlikely to list 50-ish items using this method, anyway.
I guess the logo of this site was inspired by hanko.
