I can't tell you what the original poster's intent was, but...there
definitely are some cassette decks out there with cleaning indicators.
I've seen a radio from a Honda automobile that has a lighted cleaning
indicator for its cassette deck. After some amount of time passes, the
light in the indicator goes on, at which point you're supposed to
clean the playback head and associated transport parts.

I stand corrected. I suppose car (and tractor) stereos would be the very
items to have such a display.