I can't tell from the picture, but a broody hen will growl at you when you come near, and when she gets off the nest once a day or so to eat and drink she will fluff her feathers out and growl, walk kind of low to the ground, and say "cluck-cluck" as she walks.
She will spend all day and night on the nest, getting off the nest only once a day or so. She will stop laying when she is broody.
When they are just sitting to lay their eggs, they may growl at you, but you will find later that they are walking around the yard and not tending to the nest. It can take a hen an hour or so to sit in the box to lay an egg- they wait there for the egg to get ready.