touchmark

noun2

1. •
   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. — 1988
2. •
   (no longer used, 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 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. — 1880