Mysterious term that came into inconsistent spoken usage and started appearing as graffiti (toilet walls, arenas, game arcades, etc.) in Atlantic Canada--particularly central Newfoundland--sometime in the mid to late 1970s, and had virtually disappeared by the mid 1980s.
Its meaning is not precisely clear; it may have referred to a morally loose female (as it does in other contexts), but there is also evidence of a more esoteric or person-specific meaning. It was nearly always spelled in capital letters, suggesting an anagram or, more likely, an acronym for some presently unknown term or phrase. The word was particularly associated with young fans of the more aggressive and/or occult genres of rock music, and there is reason to believe that it originated in the (former) military and airport town of Gander, Newfoundland--a community strongly associated with devout rock fans in the late 1970s/early '80s.
The word 'Slue' (or 'SLUE') is not believed to have had a regular, grammatically consistent or logical usage in common speech, yet seems to have served as more than merely a marker or qualitative term typical to most graffiti.