What is one element required for inspecting a segmented circle?

The correct choice highlights that for effective inspection of a segmented circle, it must be visible from the air. This visibility is crucial because segmented circles are typically used around airports to provide pilots with visual cues related to runway operations. Being able to see the segmented circle from an aircraft ensures that pilots can correctly interpret the indications it provides, which is vital for their navigation and safety during landing and takeoff.

In the context of the other options, while presence of signage, operational monitoring, and favorable weather conditions can be important in broader facility operations or certain inspections, they are not fundamental requirements specifically for the inspection of a segmented circle. The primary factor revolves around visibility—if it can't be seen from the air, it serves no purpose in directing pilots appropriately.