Painting yellow cross hatchings on the left side of each step would be
self
explanatory, though expensive.

Great idea, how long would that last? 20 minutes from the escalator first
being started before you have yellow paint flakes everywhere except the
steps that were painted!

If it were a serious suggestion then it wouldn't be rocket science to put it
in the recessed part of the step to prevent this happening. Clearly though
you thought about the idea a lot more than I did