I'd love a link to the memo. According to the head of the Military Post Office (link lost, sorry) military mail is supposed to have a postmark even if postage isn't required.
Furthermore, there is the [link|http://www.latimes.com/news/printedition/front/la-071501florida.story?coll=la%2Dhome%2Dtodays%2Dtimes| LA Times story ]