How is a NORAD Special Interest flight designated in the remarks section of the flight plan?

A NORAD Special Interest flight is designated in the remarks section of the flight plan using the letter "S". This designation is important because it indicates to air traffic control and other relevant authorities that the flight has garnered specific interest from NORAD, which is responsible for North American air defense. This may include monitoring for surface-to-air threats or other national security concerns, and it helps to ensure that appropriate precautions and services are provided for the flight in question.

The use of an "S" allows for the swift identification of these flights within the vast array of air traffic, ensuring that they receive the attention necessary for operational security and safety.