A locked (closed) padlock, as used to secure a latch or chain, or as an icon for a secure internet connection, private account, or locked device. Generally depicted with a gold base and silver shackle. WhatsApp’s design is silver.
Commonly used for content concerning safety, security, privacy, and protection as well as various senses of lock, e.g., locked in/down.
This emoji does not display in page titles on Apple’s Safari web browser, presumably to prevent less reputable sites from pretending to be secure (encrypted using HTTPS).
See also: 🔏 Locked With Pen and 🔐 Locked With Key.
Locked was approved as part of Unicode 6.0 in 2010 under the name “Lock” and added to Emoji 1.0 in 2015.