The correct answer is D. When a vessel is consigned to Voluntary Naval Control of Shipping, the message will refer the vessel operators to the appropriate naval authorities, not to any reference publication. The Voluntary Naval Control of Shipping is a procedure where merchant vessels are placed under the control of naval authorities during wartime or other emergency situations. This allows the naval forces to coordinate the movement and activities of civilian merchant vessels for strategic and security purposes. The message directing the vessel to this control would not direct the operators to any reference publication, but rather to the naval authorities managing the control. The other answer choices are incorrect because they do not accurately reflect the appropriate response when a vessel is consigned to Voluntary Naval Control of Shipping. The Coast Pilot, the International Code of Signals, and "C" are not the proper references in this scenario.