What the heck does "do not disturb" mean, other than, DO NOT DISTURB.

Gosh, I don't think any guest takes it to mean:
"Maybe do not disturb - I'm not really sure so call me and check or knock a few times, or assume I left in a hurry this morning and forgot to take it down, so come on in and clean the room."

Personally I think the DND sign should be an firm and open policy at hotels: printed on the inside of the door. What exactly does the hanging of the sign mean at your hotel?

I hadn't thought about what an earlier poster wrote about whether or not they changed the sheets??? Actually I'm pretty sure that this was totally made up for a new guest as the shampoo bottles and everything were replaced (like they do for a new guest). However, I did use the room and bathroom a bit before leaving, and I'll bet no one came back in after me before they rented that to the new guest! So, does make you wonder, if your room really is "new" when you check in.