In 1966, environmental-health engineer Charles Baldwin was developing containment systems for the Cancer Institute at the US National Institutes of Health. He enrolled the help of marketing colleagues to develop and test some warning symbols. Something unique; striking enough to be remembered; something memorable but meaningless – “people could be educated as to what it means”.

The biohazard symbol was initially blaze orange in colour, to be the most visible under the most conditions. It was designed to be easily stencilled, and three-sided to ensure instant recognition in any orientation. A tremendous success for Baldwin, and though colours have changed slightly, this is a powerful symbol used and understood around the world.

http://www.trustedlog.com/2008/01/28/biohazard-symbol-creation-history/