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
A California listener shares a couple of pranks from her time in the U.S. Marines, where unsuspecting recruits would be ordered to complete impossible tasks. She remembers that newbies would be sent to retrieve a bucket of frequency grease or a...
What do you call a long sandwich filled with lots of ingredients? Whether you call it a sub, a hoagie, a grinder, or something else entirely depends on where you’re from. And: Martha’s visit to an Alaskan reindeer ranch reveals why you...