Which of the following is a visual indicator used to identify overhead powerlines?

Powerline marker balls are specifically designed as visual indicators to enhance the visibility of overhead powerlines, particularly in areas where they may pose a risk to aircraft or individuals working at heights. These large, typically orange or white balls are suspended on the power lines to alert people to their presence, thereby reducing the likelihood of accidents related to contact with the lines.

While safety cones, warning signs, and reflective tape are also used for various safety indications and traffic control, they do not specifically serve the purpose of indicating the presence of overhead powerlines. Safety cones are usually used to mark off hazardous areas on the ground, warning signs are for general caution or specific dangers, and reflective tape is employed to enhance visibility in low-light conditions but does not inherently indicate the presence of powerlines. The specialized function of marker balls makes them the correct choice for identifying overhead powerlines effectively.