What distinguished marking indicates a Prohibited Area in special use airspace?

A Prohibited Area in special use airspace is indicated by a distinct blue hash mark on aeronautical charts. This designation clearly communicates to pilots that entry into this airspace is not permitted under any circumstances without specific authorizations from the controlling authority, typically for national security or safety reasons.

The use of the blue hash marks is standardized, ensuring that pilots can easily recognize these areas when planning their flights or navigating in-flight. This visual cue is important for maintaining safety and adherence to airspace regulations, as entering a prohibited area can lead to serious legal or safety repercussions.

The other markings represent different types of airspace or restrictions, but blue hash marks specifically denote prohibited areas, which is critical for pilots to understand when interpreting navigation charts.