46 CFR §45.33

1. (a)Each vessel must be marked with the diamond mark described in figure 2 of § 45.35 amidships below the upper edge of the deck line on each side with the center of the loadline mark at a distance below the deck line equal to the summer freeboard assigned under this part.
2. (b)The width of each line in the loadline mark must be 1 inch.