Mine's an abbreviation for Harley-Davidson Squirrel, "squirrel" being the nickname I earned a couple of years ago as I was told that once I grew my hair long enough to make a good ponytail, I'd be able to ride my own bike. Just as a squirrel uses its tail for balance, I would use my "tail" for the same purpose, heh.
A couple of years went by, and I grew my hair out, and lo and behold, I learned how to ride my own last year, but it's a Honda, not a Harley. The Harley will hopefully come in a few years.