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
If you take up texting and social media late in life, there’s a lot to learn! A twenty-something wants advice getting her dad up to speed on memes, Instagram, and animated images. Plus, when you’re on a long road trip, what do you call...
Elena in Mt. Holly, North Carolina, wonders why beeline means “a direct route.” Well, once a bee has gathered sufficient nectar from flowers, she flies in a straight course back to the hive. In The Journal of Henry David Thoreau, 1837...