The correct answer is B) The official number of a documented vessel is required to be permanently marked on the vessel's structure. This is the correct answer because under U.S. Coast Guard regulations, the official documentation number of a vessel must be clearly marked in a permanent manner on some readily visible part of the vessel's exterior hull or superstructure. This requirement ensures that the vessel's identification can be easily seen and verified, which is important for enforcement and administrative purposes. The other options are incorrect because the documentation number is not only required, but must be permanently marked on the vessel itself, rather than just painted on the stern or bow, or not required to be marked at all.