Which type of signs warn about hazardous conditions that could lead to serious injury or death?

The type of signs that warn about hazardous conditions leading to serious injury or death is categorized under "Danger." These signs are specifically designed to communicate an immediate risk that could cause severe consequences if not acknowledged and followed. Danger signs typically use specific colors and symbols that convey urgency and are highly visible to draw attention to the threat.

While "Caution" signs alert individuals to potential hazards that may not be immediately life-threatening, "Warning" signs indicate a situation that could lead to potential hazards but is less severe than a "Danger" sign. "Instructional" signs provide guidance or directions rather than warnings about threats. Therefore, the appropriate designation for signs indicating serious risk is "Danger," which effectively communicates the urgency and severity of the conditions present.