witness mark
n.— «We took a cursory glance around for the drill hole (witness mark) without results. The boulders previously lining the east side of the road seem to have been either replaced or built into a more solid stone wall. Several of them have drill holes through, but there’s no way of knowing which may have been the witness mark, if any.» —“Zhanna found ROON (NGS Benchmark) ” by Zhanna Geocaching Aug. 10, 2005. (source: Double-Tongued Dictionary)
Further reading
When Kentrell from West Memphis, Arkansas, worked for a granite company, his co-workers who were about to put two pieces of granite together would say I’m going to pull a seam. But why would they use the word pull for the action of pushing...
Amid court-ordered busing in the 1970s, a middle-school teacher tried to distract her nervous students on the first day of class with this strange assignment: find a monarch caterpillar. The result? A memorable lesson in the miracle of metamorphosis...