Unlike this example, these signs often had yellow arrows below the words 'fallout shelter' to indicate the direction to the shelter. It was intended to only be used with federally approved shelters. The above version of the national fallout shelter sign was introduced to the public by the Defense Department on December 1, 1961. The Office of Civil Defense originally intended fallout shelters to use the radiation warning symbol (yellow background with a magenta circle in the center of three magenta blades) but this idea was rejected because a fallout shelter represents safety whereas the radiation warning symbol represents a hazard. Use inside facilities to mark access routes to shelter areas and the shelter area itself.' The same document describes the sign shown below as follows: 'Interior sign, Type II, size 10' x 14', galvanized steel, 0.018' thick, with partially reflectorized surface and overlays. Used to mark facility entrances.' The interior signs were made of steel. The 'Posting Fallout Shelter Signs Handbook' FG-C-8.1 (June 1964) describes the sign below right as follows: 'Exterior sign, Type I, size 14' x 20', aluminum, 0.025' thick with partially reflectorized surface and overlays.

Nuclear fallout shelter sign