Probably from the resemblance of its mudguard to a Plimsoll mark
American Heritage Dictionary of the English Language, 5th Edition
From Samuel Plimsoll, a Bristol merchant.
Plimsoll Sentence Examples
They did something to meet the wishes of the publicans, Dis~drs whose discontent had contributed largely to Gladstones defeat, by amending some of the provisions of Bruces licensing bill; they supported and succeeded in passing a measure, brought in by the primate, to restrain some of the irregularities which the Ritualists were introducing into public worship; and they were compelled by the violent insistence of Plimsoll to pass an act to protect the lives of merchant seamen.
Plimsoll viaduct journey sound quiet round here Relieving cramp how large the day is.