As illustrated below, the feature currently appears under Settings > Appearance > App Icons, provided you’re on Signal for Android version 6.21.3. The ability to change app icons is nothing new for Android users, particularly for those accustomed to custom ROMs and launchers. Regardless, letting Signal users change the app icon/name directly from the app’s settings certainly cuts down a few steps. While there are only four alternate name and icon options in the form of News, Notes, Weather, and Waves, we hope Signal will offer a larger collection of icons somewhere down the line.
Signal is clearly targeting the security through obscurity angle with its latest feature addition, as changing the app icon and name to something generic like Weather or News draws less attention. This can prove to be quite a useful safeguard for people who use sensitive communication apps on shared phones or tablets, but is far from truly secure.
See https://www.androidpolice.com/signal-update-hide-app-icon-name/