A trefoil of overlapping circles, designed to be instantly recognisable as a warning for biological hazards.
Also known as: Biohazard sign
Designed in 1966 by Dow Chemical Company engineers for their containment products, the biohazard symbol was deliberately created to be highly memorable but symbolically meaningless, so its warning association could be taught rather than assumed. It became a US and international standard for labelling biological hazards.
Deliberately designed in 1966 to have no pre-existing visual associations, so its warning meaning could be taught cleanly through public education rather than relying on the shape's own connotations — described by its designers as 'memorable but meaningless'.
1966
Three identical crescent-and-circle shapes arranged around a small central circle, radially symmetric so it reads the same from any angle.
Both are internationally recognised hazard-warning trefoils, though for different hazard types and standards bodies.