Years of baseball and I never knew that. I can remember watching K counts in the outfield of MLB parks and the third K was always backwards. I figured this was to avoid having KKK on national TV. I was also 12.
Nope, it's swinging versus looking. That's the way you keep up with it in the score book if you are keeping score. Instead of writing KS or KL, you write the K either forward or backwards.