On a current stay at a mid-level hotel chain in El Paso, Texas, we left the do-not-disturb sign on the door in the morning, until we were done with breakfast, and getting ready for the day. Our room was skipped. The housekeeping staff told us that if they see the do-not-disturb sign on the door, that they would mark on their chart to skip the room for the day. I've never had a problem doing that before, and we did take down the sign by noon. Have I just been lucky several times in the past?
Excellent answers and comments. Based on them, a little more details for my situation. My wife often makes friends with the housekeeping staff, and for this particular hotel, she talked to a couple of the staff and got some more information. It's a 5 story hotel, with a broad mix of clients; families, business, etc. and the staff has to clean several floors. So in this area, they can't keep track of who/what when. So in hindsight, I should have asked. To give a feel for the hotel class, it is a Hyatt Place. Other than the confusion on my part, all was up to standards.