Super interesting article from 99% invisible (As always) about the history of the creation of the biohazard symbol.
According to Charles Baldwin, an environmental-health engineer who contributed to its development:
“We wanted something that was memorable but meaningless, so we could educate people as to what it means.”
They had several proposals and tested over 300 people which one had the less common meaning but it was the most remember, and this one was the winner. For more information about the origin, read the full article in 99% invisible website.