The sign on the handle, and what it does by day

At three in the morning a closed door stays closed by default. At two in the afternoon it does not, and this is the one genuine difference between a daylight booking and a night one. Housekeeping, maintenance, minibar checks and deliveries all happen in daylight, all of them carried out by people who hold a key to your room, and most of them announce themselves with a knock and then keep going.

Put it out before you write

The sign goes on the handle when you start arranging the afternoon, not when she is in the lift. Buildings differ in how they express it: a physical card, a switch beside the door, a setting on a room panel, or occasionally a line in an app. Find out which yours uses on the first day of the trip rather than at twenty past one on the day it matters.

The sign is not the whole answer

Two things get past it in most buildings. A scheduled maintenance visit will usually knock anyway, and a delivery to the room will too. If either is expected, say so in the thread so the time can be placed around it. The other thing worth doing is calling the desk earlier in the day to ask that the room be skipped, which is a routine request made by people who are working, sleeping off a flight or unwell, and it attracts no attention whatsoever.

After she leaves

Take the sign down if you are going out, or the room simply does not get cleaned that day and the following morning somebody arrives early to catch up. It is a small thing and it is the one guests forget. The rest of the practical ground is covered on the FAQ.