Plim·soll mark 
(plĭmsəl, -sôl′)
(plĭmsəl, -sôl′)n.
Any of a set of lines on the hull of a merchant ship that indicate the depth to which it may be legally loaded under specified conditions. Also called load line, Plimsoll line.
[After Samuel Plimsoll (1824-1898), British merchant and shipping reformer.]