Final answer:
A notification or an icon often indicates that a device is in Bedtime Mode, which reduces blue light and interruptions during sleep hours.
Step-by-step explanation:
A notification or an icon on the device's screen usually indicates the device is currently in Bedtime Mode. Bedtime Mode is a feature found typically on smartphones and tablets that aims to reduce the emission of blue light and diminish interruptions during the user's sleep hours. This feature can be scheduled at regular intervals (e.g., from 10 p.m. to 7 a.m.). When activated, it may change the display to grayscale, block notifications or calls, or turn on Do Not Disturb settings, depending on the device's capabilities and user settings.