Google has posted a new support page related to an upcoming verified boot system, which provides warnings about security at the time of booting your device.
Device owners will know that their phone or tablet is safe based on startup messages from the system check. The feature checks the Android device while booting to make sure that the OS is safe to use. If a device is not secure, a message will be shown at the time of booting and it will disappear after 10 seconds and the device will boot as normal.
At present, there are three types of warning messages that show an exclamation mark in different color accompanied by a message. The yellow warning means that the device software has loaded a different operating system, the orange warning means that the bootloader is unlocked and can’t check the software, and the red means something has been seriously modified. It is expected that these boot warnings will be added to Android M.