Which of the following is a clear indication that an officer has arrived at the scene of an incident?

The term "arrived" is a clear indication that an officer has reached the location of an incident. In law enforcement terminology, this word explicitly signifies that the officer has left their previous position and has physically come to the scene where the incident is occurring. This is crucial for communication among officers and dispatch, as it clarifies the officer's status and readiness to assess or respond to the situation at hand.

The other options may be somewhat related but do not convey the same direct meaning. "On site" could suggest presence but is more general and not typically used in official communication. "Completed" usually indicates that a task or series of actions has been finished, which does not specifically denote arrival. "Engaged" implies involvement or participation, but it does not necessarily indicate that the officer has arrived at the location yet, as they could still be responding or planning how to approach the situation. Thus, "arrived" is the most precise and effective term in the context of a police officer's presence at an incident scene.