I've gotten pretty good at excusing myself to go pump at work - knowing who will be mortally embarrassed if I say "I have to go pump" and who needs a gentle "I need to go do my thing" while picking up my bag. Most folks recognize the bag by now.
But what do you say when someone knocks on the door of the room you are pumping in? I pump in whatever conference room happens to be available. If the sign-out sheets on the doors are up to date, I mark off an hour (I only pump on my lunch break) with my name, and I lock the door, but that doesn't stop people from knocking occasionally. I feel like I have to say *something* so whomever it is doesn't assume the door got locked with no one in there and let themselves in with a key. Since I don't know who is knocking, I don't really know what would be TMI, and I don't want to say "Who is it?" because I really don't want to have a conversation at that point! I've tried "I'll be out in a minute" but that's usually not true, and makes me feel rushed. I just shouted "Occupied" the other day, but it didn't seem to really make sense.
So I'm curious what other ladies have done. The real solution is probably to get a "Do Not Disturb" sign, but some people might still knock.