Military map symbol for a friendly land unit or formation.
The cyan frame and icon were defined in APP-6A to indicate friendly unit for use over darker backgrounds in electronic display.

In APP-6, all units were represented by a rectangle with dimensions that varied from 1.5 by 1 to 1.7 by 1. The 1.5 by 1.0 frame was stated as the standard dimension for a friendly unit in APP-6A.
Own work
CdnMCG