According to the "T-Boat" regulations, the permanent marks placed on each side of a vessel forward, aft, and amidships to indicate the maximum allowable draft and trim are called __________.

Correct Answer: Option D — loading marks

46 CFR Subchapter T regulations require loading marks to be permanently marked on the hull to indicate the maximum allowable draft and trim. These marks ensure the vessel operates within its certified stability limits, preventing overloading and ensuring adequate freeboard for safe operation in the vessel's intended service area.