Germany, 3rd Reich, Military Hazard Safety Marker Flag. There were usually suspended from an "L" shaped wire holder, (see ZFC1008 for a complete kit). These small yellow flags are often confused with larger white flags and signs which were used to mark minefields. These smaller yellow flags were used to mark safe passages and corridors through a hazardous area. Hazards could include mines; gas contaminated areas or unexploded ordnance.

From the Louise Veninga Collection.
ZFC Noteworthy Flag