Deb a hen that is laying eggs will often have a brighter red comb. When they are in a slump the comb color will not be as bright red. Also the two pin bones on the back of the hen just a bit lower then the rectum will be close together on a hen that isn't laying, and farther apart on a hen that is. Those bones can be felt by holding the hen and seeing how many fingers you can place between the pin bones.
