Adopted by NATO in the early 1980s, the Marker Set, Contamination, NBC was designed to be used by soldiers in the field to mark out areas contaminated by nuclear, biological, and chemical weapons.
SOURCES:
TM 2-9905-001-10: Operator’s Manual for Market Set, Contamination: Nuclear, Biological, Chemical (NBC) (9905-12-124-5955), Headquarters, Department of the Army, August 1982
https://armychemicaloperations.tpub.com/CM7114B/Part-A-Nbc-Contamination-Markers-5.htm
https://www.groundzerobooksltd.com/pages/books/81638/united-states-army/marker-set-contamination-nbc
https://www.trngcmd.marines.mil/Portals/207/Docs/TBS/B2I0413XQ-DM CBRN.pdf?ver=2015-12-22-084156-727
https://www.scribd.com/presentation/597041914/NBC-marking-Kit
https://talesfromthesupplydepot.blog/2020/04/27/nbc-marker-signs/
https://blueshield.es/wp-content/uploads/2022/07/380180eng.pd
