What is a common indicator of improper elevator rigging?

Unusual pitch behavior during flight serves as a significant indicator of improper elevator rigging because it directly relates to how the aircraft responds to control inputs regarding its pitch attitude. Elevators are critical control surfaces that manage the upward and downward motion of the aircraft. When the elevators are rigged incorrectly, the pilot may experience unexpected or erratic responses, such as delayed or overly sensitive pitch changes, which can lead to difficulty in controlling the aircraft effectively.

The other options, while they may indicate other issues, are not as directly related to elevator rigging. Excessive vibration of the control yoke could stem from a variety of issues, such as engine problems or other control surface malfunctions, rather than a direct result of elevator rigging. Decreased fuel efficiency usually points towards aerodynamic inefficiencies or engine performance issues, and poor visibility from the cockpit typically relates to obstructions or design rather than control surface rigging. Thus, unusual pitch behavior is the most relevant sign of rigging problems with the elevator system.