This is an emoji with an index finger on the mouth as if making a "shush" sound. It is generally used asking others to be quiet or keep a secret, sometimes it also has a little sneaky meaning. Related emojis: 🤭, 🙊.
When you try to tip classmates up in class, you can say,"🤫 Watch out! I heard the sound of Miss Lee's high heels 👠❗️" I was hungry in the middle of the night and sent a message to my brother, "Let’s order takeout, and don’t let 👩mother know 🤫" When you share the little ㊙️ secret with friends, you can say, "I think I like that boy, but don’t tell him 🤫"