This kind of crap bugs me:
I saw this at all three hotels I stayed at in California, in varying forms, though this is the most obnoxious:
Conserve! Thank you for your participation in this initiative that better serves the environment.
If I believed for one second that these hotels cared, I guess it would be different. However, what the hotels are really saying is “prevent us the labor and expense of washing and changing the sheets” not "we care about the environment.
Leave it to the guest to make an educated decision. Provide a card, and say “if you leave this card on your bed, we will change the sheets, otherwise your bed will just be remade.” Leave it at that, and stop trying to guilt people into a certain behavior because it’s to your benefit.