Which safety notation indicates the potential for serious injury or death if not observed?

The safety notation that indicates the potential for serious injury or death if not observed is "Danger." This term is used in safety communications to alert individuals to an immediate hazard that could result in severe consequences, such as serious injury or loss of life. It serves as a critical warning to take specific actions to avoid these risks.

In contrast, "Warning" typically signals a risk of injury but not necessarily of a potentially fatal nature. "Caution" indicates a lesser risk, often related to property damage or minor injury, and "Note" is generally used for informational purposes and does not imply any hazard. Understanding these distinctions is vital for ensuring safety and compliance during the operation of the M9 Service Pistol and in following proper safety protocols.