This question already has an answer here:
Tipping overseas guide for Australians: 10 mistakes to avoid mentions tipping cleaners:
Forgetting the cleaners
It seems ridiculous to you and me, but in the US, and Canada, and many parts of the Middle East, hotel guests are expected to leave money out – the equivalent of a few dollars per day – for the housekeeping team. You'll never see these people, but the cleanliness of your room will certainly increase with the more money you decide to leave.
How do you indicate what money is (and is not) intended as a tip to the cleaners in hotels and motels (in the United States if it needs to be narrowed down to a specific country)?
The question How to tip housekeeping in hotels if leaving tips daily? more or less answers my question, but doesn't address whether cleaning staff may inadvertently interpret money left lying around that wasn't meant as a tip as one.