Whatever you do, whether it be in a premade "Mousekeeping" envelope, with a little note, or under the housekeeper card that they leave welcoming you to the resort, make sure you leave something to designate the cash is for the housekeeper. On our last visit, I left $5 on a table in the middle of the room without any indication that it was for the housekeeper. When we got back from the park around 1 pm for a little pool time, we came back to a clean room, with a brand new towel animal, and the cash sitting right where I left it. I ended up tracking the housekeeper down and giving her a $10 spot for both the great job on the room, and for her honesty. In an unsure situation, instead of pocketing the cash, she left it. I think that's something that's easy to appreciate.