You will get different answers but it my opinion, it depends. if a person dies in service, or retired from the regular force, or was a long term reservist, or for any other reason used the rank during his life, then use his rank. It grinds my gears when people bring their own prejudices into who deserves the title or not.
Also, use appropriate abbreviations without a period at the end. Use the country specific abbreviation. For example, I was a Capt, not a CPT.