Scene: I've put the DND hang-tag on the door, at night, before I go to sleep. Next morning, early (well, too early by *my* standards!) there's a knock at the door. Since I know that I've put out the DND sign, I ignore the knock. A moment later, someone with a key is beginning to open the door.

Me: (grabbing room phone and dialing operator, and then, in the most pitiful voice I can manage): "I need security and police!! Someone is breaking into my room!!)

Operator: (in a calm, sweet tone): "Oh no, Sir, that's just housekeeping."

Me: "It can't be!! I have the Do Not Disturb sign on my door!!"

I presume that in each of the two hotels that I've had to do this in (that I return to frequently), I have a "permanent record", in which they have recorded the fact that I have this strange notion that "Do Not Disturb" actually means "Do Not Disturb"....because at each of them, it's never happened again.