When hens are broody they'll let you know. They'll get on a nest of eggs and they'll sit there all hunched up and protective looking, very different then when laying (they sit more upright generally when laying). They may even peck at you and when they get off the nest they spread out all their feathers and run all over the place on their toes, telling any roosters to get out of their way. They'll only use the bathroom once a day, then go running back to their nest. If someone else is on their nest they'll wait near-by until they get it back.
Broody hens are awesome!
I have one right now also.