World War II postal acronyms
Terry Pratchett parodied this briefly in his Discworld novel "Going Postal" . 
<triplet> Terry Pratchett <subj> Discworld <obj> notable work <triplet> Discworld <subj> Terry Pratchett <obj> author <triplet> Going Postal <subj> Terry Pratchett <obj> author <subj> Discworld <obj> part of the series