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
How do you transform ancient Chinese script for use in the modern age? English uses a keyboard with just 26 letters, but the first Chinese typewriter looked like a small table under a huge disk with more than 4,000 characters. A new book chronicles...
What’s up with ketchup? The shifting history and spelling of the name of this condiment. For centuries, ketchup was a fishy sauce originating in Asia—the tomatoes came only later! Plus, a new book shows what’s lost when a language dies: when there...