The zipper-mouth face emoji is a yellow, neutral face with a furrowed brow, a small frown, and a single, vertical line in place of a mouth, shown with a zipper mouth as if it has been sealed shut.
It is often used to convey a sense of secrecy, confidentiality, or silence, and it can be used to show that you are keeping something to yourself or that you are being quiet. It can also be used to express a sense of frustration or irritation, or to show that you are feeling silenced or censored.
Google's design for ? Hushed Face previously featured a zipper-mouth.
Zipper-Mouth Face was approved as part of Unicode 8.0 in 2015 and added to Emoji 1.0 in 2015.
U+1F910
? Zipper-mouth face