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.?

The Secret History of Typography in the Oxford English Dictionary ? The Bygone Bureau