Meaning
An old-style smiley with closed curved eyes, pink cheeks on many platforms and a calm smile. The character itself is much older than modern emoji, which is why some fonts still show it as a small black-and-white outline.
Its mood is relaxed, content and a little bashful, close to the smiling-eyes face: “Had a quiet Sunday with tea and a good book ☺️” It suits gentle thanks and peaceful updates. If an app shows the plain text version instead of the colorful one, it can look a bit old-fashioned, but the meaning stays the same.