countermark

from The Century Dictionary.

• To add a countermark to, in any sense of t hat word.
• noun A mark or token added to a mark or marks already existing for greater security or more sure identification, as a second or third mark put on a bale of goods belonging to several merchants, that it may be opened only in the presence of all the owners; specifically, the mark of the Goldsmiths' Company of London, added to that of the artificer, to show the metal to be standard.
• noun A small device, inscription, or numeral, stamped upon a coin subsequent to its issue from the mint.
• noun An artificial cavity made in the teeth of horses that have outgrown their natural mark, to disguise their age.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To apply a countermark to.
• noun 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.
• noun (Far.) An artificial cavity made in the teeth of horses that have outgrown their natural mark, to disguise their age.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A mark or token added to those already existing, as a security or proof.
• noun An artificial cavity made in the teeth of horses that have outgrown their natural mark, to disguise their age.
• verb transitive To apply a countermark to.