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
She sells seashells by the seashore. Who is the she in this tongue twister? Some claim it’s the young Mary Anning, who went on to become a famous 19th-century British paleontologist. Dubious perhaps, but the story of her rise from seaside...
One of the most powerful words you’ll ever hear — and one of the most poignant — isn’t in dictionaries yet. But it probably will be one day. The word is endling, and it means “the last surviving member of a species.” The...