As a kid (ok, as an adult too), I knew what the "CH" on floppies meant. I was curious, but never asked or tried looking it up.

I forget when, but one day, it dawned on me that it said "HD"!

I guess most of my floppies had their labels on in such a way that the flap/door was facing down, so it said "CH". To read "HD," then the label would be upside down.