Mine is the result of doodling in my very first college class -- U.S. History, part 1 -- waaaaay back in '89. There was lots of time to doodle, in spite of the fact that it was a summer class, and only lasted six weeks.
It just kinda grew out of the doodles, and I decided I liked it, and here I am still using it twenty years later.
... now I feel old.