The symbol that recruited

measured, failed, replaced

Unicode: U+2620 skull and crossbones · Mr. Yuk is not encoded
The job: Stop a child who cannot read from drinking what is in the bottle.
Standards: The skull carries no standards force in this role; GHS retains it for acute toxicity in an occupational setting, where the audience is trained. The child-facing case has no standard at all — which is how a regional hospital came to design the replacement.
Failure modes: The failure was measured, which is what makes this the department’s most useful entry. The Pittsburgh Poison Center found in 1971 that small children were drawn to the skull rather than warned by it — it belonged to pirates, adventure and, locally, a baseball team — and commissioned a scowling green face instead. Mr. Yuk then failed in a different direction: it stayed a Pittsburgh institution and never became national, let alone international, so whether a child meets a warning designed for children depends on where they live. Green was chosen as unappealing, and has since become the standard colour of every product claiming to be natural and safe.
Cultural flips: The skull is a memento mori on a tomb, a threat on a flag, and a hazard on a bottle, and the three readings actively interfere. A mark cannot repel one audience while being adopted as fashion by another — and the audience that must be repelled here is the one least able to tell the readings apart.

Sources · 3

documented The Pittsburgh Poison Center at Children’s Hospital of Pittsburgh, 1971 — the finding on children’s response to the skull, and the commissioning of Mr. Yuk.
documented The GHS acute-toxicity pictogram, which retains the skull for occupational use.
documented The Atlas entry for the skull and its three careers (→ SYM·0100).