A documented vessel's name is marked on a clearly visible exterior area of both sides of the bow and on the stern in block letters not less than __________.

Correct Answer: Option C — 4 inches in height

46 CFR 67.123 requires that the name of a documented vessel be marked on both sides of the bow and on the stern in block letters not less than 4 inches in height. This ensures the vessel is clearly identifiable for regulatory, safety, and law enforcement purposes.