Mandatory instruction signs are used to identify runway designations, holding positions, NO-ENTRY areas, and obstacle- free zones, where pilots must receive further ATC clearance to proceed. At uncontrolled aerodromes, pilots are required to hold at points marked by these signs until they have ascertained that there is no air traffic conflict. Mandatory instruction signs have white letters, numbers, or symbols against a red background and are installed on both sides of a taxiway or runway, unless it is physically impossible to do so and provided that an equivalent painted sign marking is provided on the taxiway or runway.
