when my bunny karma is stressed she'll flip stuff all over the place and rip her fur out and chew it like as if she were getting ready to have babies.
if rabbits are stressed they will usually bang their back feel on the floor or run when you go near them and not eat, pull out hair ect, :)
Generally in most pets, some signs of stress are not eating, not sleeping, losing patches of hair and just seeming uneasy and afraid.
jlw82 is right but I just wanted to add that losing patches of hair in female rabits at least could also be a sign of pregnancy.
probably teh moment you lock them in a cage