I'm psychic. It's really not too far from the truth. Meg doesn't stand at the door, or bark, or scratch, or anything. She sort of wanders by the door. The first time my mother saw me catch it, she was like "THAT'S her signal to let her out?"
But honestly, I doubt I let her out more than twice a week or so. She goes everywhere with me, and goes to the bathroom when we are already outside. She almost never asks to go out at home.