ISO 21482 is a standard that specifies a warning symbol to warn against the dangers of radiation. The warning is made of the trefoil on the top, which warns against radiations. There are lines towards the bottom. On the bottom left, there is a skull, which warns against poison. On the bottom right, there is a running figure, and an arrow pointing outside the sign. The color red was chosen because children said it expresses danger better than yellow. The Gallup Organization recommended the symbol, after showing it to 1650 people. 