An anchored vessel servicing an aid to navigation shows which lights?

An anchored vessel that is servicing an aid to navigation displays three lights in a vertical line, with red lights on the top and bottom and a white light positioned in the middle. This configuration is established under the navigation rules to indicate the specific activity of the vessel and ensure visibility to nearby watercraft.

The red lights signal that the vessel is not on the move and is likely engaged in servicing the aid to navigation. The white light indicates the presence of the vessel and provides additional visibility. This combination not only helps other vessels ascertain the type of work being undertaken but also promotes safety in these operational waters.

The other options do not represent the correct signaling for an anchored vessel servicing an aid to navigation. For example, only using red lights or only white lights would not provide enough information to other vessels regarding the vessel's status and activity. Using two red and one green light would also be incorrect, as green typically indicates the starboard side of a vessel under way, which would not be applicable in this case.