It’s your middle finger ㅗ

It is one of the Korean vowels, which has an 'o' sound when pronounced.
If you send 'ㅗ' over text to somebody, you are showing the middle finger to him/her.

A Korean vowel pronounced like 'oh'. It requires at least one; at most three Korean consonant(s) to complete a letter. However, it is solely used to flip people off when texting.

A Korean vowel that is usually used by itself if it is to flip someone off when texting due to its resemblance to a "middle finger".