"oDWJr" (and similar) means "obligatory Diana Wynne Jones reference". I suppose oDWJm means "obligatory Diana Wynne Jones mention". It translates as "I know this subject is way off topic but I can drag in a remote reference to DWJ or her work and thus justify mentioning it on this list." Example: "I dislike that person. He reminds me of Archer. (oDWJr)"