Gesicht Mit Reißverschlussmund

A yellow face with simple, open eyes and a closed zipper for a mouth. Meaning widely varies, but commonly conveys a secret or that someone will keep one (e.g., My lips are sealed). May also be used to tell someone to stop talking (e.g., Zip it! or I’ll shut up now).

Google's design for 😯 Hushed Face previously featured a zipper-mouth.