What signifies being established on course rules in case of VFR NORDO?

Being established on course rules in the context of VFR NORDO (Visual Flight Rules, No Radio) means that an aircraft is maintaining its intended flight path and operational requirements without the ability to communicate over the radio. The correct option, which involves radar identification with approach, is significant because it establishes that the aircraft's position has been confirmed and monitored by air traffic control. This confirmation allows for a safer and more coordinated integration of the non-communicating aircraft into controlled airspace, ensuring it adheres to the necessary flight rules and regulations.

In contrast, visual clearance from the tower does not guarantee the flight path is established as it relies solely on visual verification without the element of radar tracking. A position report from adjacent traffic, while useful for situational awareness, does not establish the aircraft's adherence to course rules on its own, nor does it confirm radar identification. Lastly, flying below 3500' MSL is a parameter that might apply to certain flight operations but does not inherently establish compliance with course rules for VFR NORDO operations. Overall, radar identification is essential for ensuring the safety and coordination of non-communicating flights within controlled airspace.