APP-6A/MIL-STD-2525A-B symbol frame for affiliation: assumed neutral (this affiliation is currently missing from the standard); battle dimension: ground (installation). Strictly speaking, field AC (Installation Graphic Modifier) isn't part of the frame, but it is more convenient to render it as such. The question mark "?" belongs to field E (Frame Shape Modifier).
APP-6A, MIL-STD-2525B Change 1
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