In Baltimore, I had the habit of letting boys know that I was coming into the bathroom by thumping on the door and kicking it. I didn’t want shy bladders or mirror-gazers to be embarrassed by the presence of a teacher.
The door to the boys bathroom at school here is always propped open, so I can’t bang on it while entering. But the threshold of the door is metal, and it’s a little loose, so all I have to do is give it a good stomp. It makes a loud noise, and my presence is announced.