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Citing usage from 1949, the OED calls this mark the dog’s bollocks, which it defines as, “typogr. a colon followed by a dash, regarded as forming a shape resembling the male sexual organs.” This is why I love scrounging around the linguistic scrap heap that is the OED. I always come across a little gold. And by “gold,” I mean, “vulgar, 60-year-old emoticons.”
(via The Secret History of Typography in the Oxford English Dictionary – bygonebureau.com)
A great article for budding archetypists and palaeotypographists!
I actually use punctuation like that :- now I’ll have to consider censoring my punctuation (or should I just snigger under my breath?)