(A) : Danger signals are made of red colour. 
(R) : Scattering of light is minimum for red colour

Danger signals are red in color because it is scattered the least by air molecules. The effect of scattering is inversely related to the fourth power of the wavelength of a color. Since the color red has the highest wavelength of all the colors we can see it scattered the least. 

So, red light is used as a danger signal as it is able to travel the longest distance through the fog, rain, etc.