Some hens show broody symptoms to a greater or lesser extent than others. However, the "typical" broody behaviour is that she will not leave the nest box more than once a day voluntarily (whether there are eggs under her or not), and if disturbed she will put up her hackle featers and screech at you. Many hens will pluck their breast feathers out to make a 'broody patch' on their chest. While walking about to get her food or whatever, she will making a tick-tick-tick sound (or for australorps, bop-bop-bop), which is why some people call them clocking hens. Other hens will aim the odd peck at her and she will very likely raise her hackles and possibly scream at them too. She will not lay eggs, though I have noticed that some lay one final egg at the beginning of being broody. I have some hens who are more polite about it though, and one or two who actually look a bit apologetic. My way to break this behaviour is to either put her in a wire-bottom cage (to cool their underside) and only let them out once a day until they go off the idea, or put them in a seperate pen where there is no nesting box or nesting place. Other ideas are ice-cubes under them in the nestbox instead of eggs (which works for some but not others), dunking them in cold water to cool the breast . . . . . . but absolutely NOT the old fashioned way of putting them in the dark without food and water for 2-3 days.
