it is never (and i do mean never) appropriate for housekeeping to ignore a DND sign within the "rules." what i mean by that is that housekeeping should honor the sign until the checkout time for the guest. if the guest requested a 4 PM checkout and it was honored, the room should not be entered until 4 PM. and, if the guest is not scheduled to checkout, the room should not be entered.

period.

the better starwood hotels will simply slide a note under the door that they tried to clean the room but honored the sign. they ask you to call Service Express when you are ready to have the room made up. lower end starwood properties aren't as nice.