Example
Before
Bubble letters 123
After
Ⓑⓤⓑⓑⓛⓔ ⓛⓔⓣⓣⓔⓡⓢ ①②③
Uppercase only for some styles
Unicode includes circled versions of both uppercase and lowercase letters, but black bubbles and squares exist only as capitals, so lowercase letters are converted to capitals in those styles.
Things to know
Screen readers may read these characters oddly or skip them, and search engines don’t treat them as ordinary words. Use them for a word or two of emphasis, not for whole posts, usernames you want people to search for, or anything that needs to be accessible.