Not bearing an identifying mark: an unmarked police car; unmarked merchandise. (adjective)
Not observed or noticed.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "unmarked" in a sentence
"This was a blind test, with two groups of tasters sampling beer in unmarked cups."
"His sons died prematurely and are buried in unmarked Sonoma County graves."
"Not that other DC agencies, the courts, or police are much better — ped rights in unmarked crosswalks are ignored on all sides, there are few (if any) arrests for failure to stop and give right of way, no matter how aggressive the drivers involved have been."