Military map symbol of a hostile unit or formation. 
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 colour red has been used to distinguish hostile entities since the original APP-6 standard. APP-6 used a rectangular frame for all units, but in APP-6A the rectangular frame was replaced with a diamond frame for hostile units.
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CdnMCG