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. The above version of the national fallout shelter sign was introduced to the public by the Defense Department on December 1, 1961. It was intended to only be used with federally approved shelters. Unlike this example, these signs often had yellow arrows below the words "fallout shelter" to indicate the direction to the shelter. In 1962, contracts were negotiated for the production of 400,000 aluminum outdoor signs and one million steel signs for indoors.