How is a Mode C Intruder indicated in radar displays?

In radar displays, a Mode C Intruder is indicated as Unpaired LDB (Layer Data Block). This representation is essential for air traffic controllers to differentiate between aircraft that are equipped with a Mode C transponder, which provides altitude information, and those that are not. The Unpaired LDB indicates that there is a target that does not have a transponder reply — essentially providing a warning that an aircraft's altitude cannot be determined, which is crucial for maintaining safe separation between aircraft.

The other methods mentioned do not specifically relate to how a Mode C Intruder is identified. A beacon code pertains to a transponder reply used for identifying tracked aircraft, flashing lights are not a standard method for indicating radar intruders, and frequency does not directly correlate with the identification of a Mode C Intruder. Thus, the Unpaired LDB serves as an essential tool in radar operations to ensure safety in controlled airspace.