During a nighttime navigation, what additional light may a tug under 50 meters show while pushing?

A tug under 50 meters in length that is pushing a vessel is permitted to display another masthead light to indicate its status while engaged in towing operations. This additional masthead light serves to enhance visibility and improve the identification of the tug's specific activities during nighttime navigation. It is essential for the safe navigation of vessels in proximity, as it helps other mariners understand the tug’s intentions and maneuverability.

Displaying an additional masthead light is important because it signals that the tug is not just traveling under its own power but is also engaged in propelling another vessel. This is critical for the other vessels on the water, ensuring they can take appropriate action based on the tug's configuration and movement.

Other options would not provide the same level of clarity or adherence to the COLREGs. Flares are emergency signaling devices and not permanent navigation tools. A red light would not correctly represent the operation of a tug. Finally, not displaying any additional lights would not comply with navigation safety practices, potentially increasing the risk of collisions.