(1):
(n.) A mark or token added to those already existing, in order to afford security or proof; as, an additional or special mark put upon a package of goods belonging to several persons, that it may not be opened except in the presence of all; a mark added to that of an artificer of gold or silver work by the Goldsmiths' Company of London, to attest the standard quality of the gold or silver; a mark added to an ancient coin or medal, to show either its change of value or that it was taken from an enemy.
(2):
(n.) An artificial cavity made in the teeth of horses that have outgrown their natural mark, to disguise their age.
(3):
(v. t.) To apply a countermark to; as, to countermark silverware; to countermark a horse's teeth.