Final answer:
The skull and crossbones is the most suitable symbol for highlighting critical safety information as it historically denotes serious hazards.
Step-by-step explanation:
The symbol most suitable for highlighting critical safety information is the skull and crossbones. This symbol has been historically used to denote poisonous substances and other dangers that could cause death or serious harm. It effectively communicates a strong warning to proceed with caution and to recognize the presence of a significant hazard. In contrast, symbols like checkboxes, thumbs-up, recycle arrows, and various other icons do not convey the same level of urgent warning as the skull and crossbones does.