The correct answer is A) Certificate of Documentation. The official identification of a vessel is found in the Certificate of Documentation, which is issued by the U.S. Coast Guard. This certificate serves as the official registration document for the vessel and includes key information such as the vessel's name, hailing port, official number, and other identifying details. The other options, such as the Classification Certificate, Certificate of Inspection, and Load Line Certificate, while important documents, do not contain the official identification of the vessel like the Certificate of Documentation does.