The problem is that despite a DND sign, in many hotels housekeepers pound on the door anyway. When one answers and points to the DND sign (still highly visible on the doorknob from the hallway), they just shrug and don't even apologize. It's disgusting and extremely annoying. If this is the hotel policy, the policy should be published rather than the hotel just supplying DND signs *as if* they will be honored by stuff.