The phrase “to toe the mark” means: To conform with the rules or to standards of discipline; to fulfil one’s obligations; to come up to scratch.
Literally, this used to be a term in footracing, now replaced by the command “Take your marks.”
An order, that is, to all entrants in a race to place the forward foot on the designated starting line. The expression does not appear to be more than about a hundred and fifty years old and could have been of American origin.
At least the earliest use thus far found is in James K. Paulding’s The Diverting History of John Bull and Brother Jonathan (New York, 1813).