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
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