Which of the following behaviors signifies alerting in narcotics detector dogs?

Indicating is a crucial behavior in narcotics detector dogs that demonstrates their ability to identify the presence of narcotics. When a dog alerts to a narcotic substance, it typically does so through specific actions such as sitting, lying down, or performing a nose point toward the area where the drug is located. This behavior signals to the handler that the dog has detected something of interest, allowing for further investigation.

Other behaviors like ranging, exiting, and pinpointing do have their own contexts in dog training and detection scenarios, but they do not directly reflect the alerting process. Ranging refers to a dog moving away from the handler to search for scent, exiting might indicate leaving an area, and pinpointing may involve focusing on a specific location without a clear signal of detection. Thus, indicating is the definitive behavior that signifies an alert in narcotics detection.