https://www.seawarstore.com/NavalEnsignsDlx.htm
This site offers dedicated military flags that are placed on the table for each player.
Here are my versions of:
Operation: Market Garden
http://axisandallies.metalsaber.com/Market.jpg
Operation: Sealion
http://axisandallies.metalsaber.com/Sealion.jpg
Operation: Downfall