An Indicator Light, which is attached to all buildings that have a power connector.
Indicator Lights are tube lights situated on all electricity-powered and generator buildings that reflect the building's operating state. There are five total operating states they can display. Indicator Lights have a hitbox and cannot be walked through, but structures such as walkways can be built through them if they aren't within the hitbox of a building.
The only exception are Crash Sites and the AWESOME Sink, which have a power connector but lack Indicator Lights.