Military map symbol for a unit or formation of unknown alignment. 
This symbol employs the Assault modifier from the US standard in ADP 1-02. The modifier was intended to be used with the aviation icon to indicate air assault lift helicopters. It is instead used with the armoured icon to indicate armoured assault personnel carriers. Symbols such as this would be used for armoured personnel carrier units, such as Canadian Kangaroo units of the Second World War or modern day Assault Amphibian Battalions of the USMC. 

The original APP-6 standard depicted all units within rectangles and had no indicator for forces of unknown alignment. Use of yellow and quatrefoil shaped frame were both introduced in NATO's APP-6A standard to denote a entities of unknown allegiance.
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CdnMCG