Refer to the current Seattle sectional excerpt near Camano, Washington. A boxed notice there reads: "FOR REASONS OF NATIONAL SECURITY, PILOTS ARE REQUESTED TO AVOID FLIGHT AT AND BELOW 2900' MSL IN THIS AREA." What kind of airspace feature is this?

Why: National Security Areas are established around sensitive ground facilities and are shown on sectional charts with a boxed advisory notice asking pilots to voluntarily avoid flight below a stated altitude, rather than a hard regulatory boundary — flight within an NSA is not necessarily prohibited, but is strongly discouraged by the FAA for the reason stated on the chart.

• MOAs are military training airspace shown with a named, hatched boundary (such as "Mt Dora West High and Low MOA"), not a request-style national-security notice box.
• A TFR is a temporary restriction published by NOTAM for a specific, time-limited event — this is a standing printed chart notice, not a temporary one tied to a NOTAM.