A note like that is effectively blackmail and would "insure" that I would tip 0.

BTW, a few years ago, I learned at the Sheraton in San Diego, that the housekeeping manager made a sweep of all the rooms before anyone cleaned them. Whether she kept all of the tips was not clear. But I subsequently heard that this is common practice. So I always try to spot my actual cleaner and tip him/her directly rather than leaving anything in the room