touchmark

noun

1. (archaic)The manufacturer's official identifying sign, impressed into a pewter object.

   “For quality control, Parliament in 1503 required all London-made pewter to be stamped with the maker's symbol or touchmark.”

2. (archaic, rare)A symbol, sign, or other inscribed indication used to aid the alignment, calibration, or other adjustment of a measuring device or scientific instrument.

   “The instrument used was a refracting telescope by Dollond. . . . The cap containing the diaphragm was furnished with a touch-mark consisting of a projecting spoke. When in adjustment as described above this mark was parallel to the short side of the parallelogram.”

   “The initial touch-mark was established at Roper's saw-mill, on the North River, and is a point on 20-penny nail driven flush with the horizontal surface of sill to bull-wheel.”