What is the proper courtesy when an officer is traveling in an official vehicle?

When an officer is traveling in an official vehicle, the proper courtesy is to salute the vehicle. This gesture is a sign of respect and recognition for the authority and rank that the officer represents, even when they are not present in a formal setting. Saluting the vehicle acknowledges the position of the officer and upholds the decorum expected in military and law enforcement contexts.

Saluting is a traditional military practice that signifies respect, and it retains its significance whether the officer is on foot or in a vehicle. This action reflects an understanding of the customs and courtesies that are important in maintaining a respectful environment within the ranks.

The other choices involve actions that may not be appropriate or recognized as proper military or law enforcement protocol. For example, standing at attention or standing at ease doesn't convey the same respect in the context of a passing vehicle, and waving might be seen as overly casual or informal for the occasion. Thus, saluting the vehicle is indeed the correct and recognized form of courtesy in this situation.