Meaning
One eye closed in a wink, the other open, with a small smile. A wink adds a private signal to a message: “I’m joking,” “you know what I mean,” or a bit of flirting, depending on who is talking to whom.
Among friends it softens teasing and inside jokes: “Don’t worry, your secret about the karaoke night is safe with me 😉” Between people who are not close, especially at work, it can feel suggestive or overly familiar, so it is better left out of messages to managers, clients or someone you have only just met.