Just invest in some masking tape or post it notes or something.
You get the same ‘Aha! A stranger will see this and be inspired!’ possibility, and it will take a cleaning person approximately .005 seconds to peel it off when it’s their job to do so.
Also, maybe someone who really needs it will take the note with them and put in in their pocket to look at again and again.
How is that not a million times better than ruining a cleaning person’s day with difficult-to-remove graffiti?