Wiktionary
red tag
n. One of the plastic cards used in the kanban manufacturing system.
Usage examples of "red tag".
But there was also a red tag, which meant neurosurgery, and a yellow tag, which meant intensive care, and a white tag, which Morris had almost never seen on a patient's chart.
The computer, faster than any human, displayed a red tag for each invader, moving through the schematics of the cruiser.
When her orders were confirmed by Terok Nor Ops, she was given a large red tag to wear around her neck, certifying she had permission to be in the complex.