witness mark
n.— «When recovering evidence for further observation, preservation of any dirt or grease mark on samples can be vital if critical evidence of its past history is not to be lost. Such trace evidence (witness marks) can help in reconstructing past movements of the sample, such as contact with older, perhaps mating parts.» —by Peter Rhys Lewis, Ken Reynolds, Colin Gagg Forensic Materials Engineering: Case Studies Sept. 29, 2003. (source: Double-Tongued Dictionary)
Further reading
Enthusiastic book recommendations! Martha’s savoring the biography of Alexander von Humboldt, the 19th-century explorer, polymath, and naturalist who revolutionized our understanding of nature and predicted the effects of human activity on...
We use the term Milky Way for that glowing arc across the sky. But how people picture it varies from culture to culture. In Sweden, that starry band goes by a name that means “Winter Street,” and in Hawaii, a term for the Milky Way...