Military symbols provide an alternative to the profile icons used in TripleA,
Contemporary NATO symbols can be found in File:App-6aHandbook.pdf.
For late cold war, see APP-6.
The symbols used during the Korean War can be found here .
The navy does things differently in MIL-STD-2525. Pages 7-9 are most useful.
If you are using military symbols I would suggest putting the nation's flag immediately below the unit symbol at the same size.
These symbols are contemporary symbols from HistoryOfWar.org. Good treatment of air & naval forces.
From The Armchair General
From Decision Games
Some individual symbols
There is a good page at Wikimedia