Crossbones (noun)

A symbol of danger or death, typically depicted as a skull with two bones crossed behind it.

Origin:

From the two bones which form the shape of a cross, typically depicted as skull and crossbones.

Examples:

1. A warning sign with crossbones indicates a hazardous area.
2. The pirate flag had a skull and crossbones on it.
3. The crossbones on the bottle of poison warned of its deadly contents.
4. The crossbones are a symbol of death and danger.
5. The crossbones are used as a warning symbol on many hazardous materials.