Rule 29 - Pilot Vessels
(a) A vessel engaged on pilotage duty shall exhibit:
(i) at or near the masthead, two all-round lights in a vertical line, the upper being white and the lower red;
(ii) when underway, in addition, sidelights and a sternlight;
(iii) when at anchor, in addition to the lights prescribed in Rule 29(a)(i), the light, lights, or shape prescribed in Rule 30 for vessels at anchor.
(b) A pilot vessel when not engaged on pilotage duty shall exhibit the lights or shapes prescribed for a similar vessel of her length.
Those traveling the C&D Canal will see this when a ship is approaching Chesapeake City. White Over Red Pilot Ahead. I guess I should do a list of these rhymes we use to help remember the nav lights.