Symbols that warn of danger
Symbols whose documented purpose is to signal danger to whoever sees them — drawn from chemical labelling, biological and radiological safety, and automotive instrumentation, which are entirely separate regulatory traditions that happen to share this one communicative job.
These marks warn about very different kinds and degrees of danger, and none of them is a general-purpose 'danger' sign: a red dashboard tell-tale means 'stop driving and check this', a GHS pictogram classifies a chemical property, and the radiation and biohazard trefoils mark a controlled hazard area. Read each symbol's own entry for what it actually requires you to do — do not treat membership of this grouping as equivalence.
Safety & hazard
GHS skull and crossbones pictogram
A black skull and crossbones in a red-bordered diamond, the GHS symbol for acute toxicity.
Safety & hazard
Biohazard symbol
A trefoil of overlapping circles, designed to be instantly recognisable as a warning for biological hazards.
Safety & hazard
Radiation warning symbol
A three-bladed trefoil, conventionally black on a yellow background, warning of ionising radiation hazards.
Vehicle dashboard
Brake system warning light
A red circle-and-exclamation-mark dashboard icon, often flanked by curved brackets, warning of a parking-brake or hydraulic brake-system fault.