Mine had some lice earlier in the season and they were quite obvious. If you catch a couple of the hens (easier than grabbing your man again), look around the base of their feathers in the vent region. Lice eggs sort of cluster at the base of the feather - they just look like a little mass of white stuff. Like this:
http://d1j96f25uhu3hg.cloudfront.net/images/health/Lice-Eggs-Chickens.jpg (hope that link works!)
On the whole lice shouldn't give a chicken too many problems beyond being a bit irritating. Have you got a good dust bath for them? If they've made their own, try adding a bit of wood ash to it - that can help with mites for sure and I think maybe lice as well. If you're going to dust, you need to use a powder with an active ingredient in it - Permethrin was the one my vet told me to look out for and you can get it on line (the one I got was for aviary birds though so I binned the eggs for a couple of days just in case).
Red mites are very tenacious and can require drastic measures but they don't live on the bird. To look for them, check at the end of the perches for little scurrying dots of red or grey. They were marginally bigger than I was expecting but the first time I saw them was in a heaving mass underneath a broody so they were very obvious

. Then I knew what to look for - and I have since seen a few in the main hen house at which point I creosoted. The diatomaceous earth also helps break their life cycle so it's not a quick fix but helps prevent them building numbers.
The other common(ish) mite is a Northern Fowl mite which I think can live on the bird but will also be affected by permethrin. I think they're slightly bigger than red mites and can generally be seen around the vent area.
I'd try and powder/dust bath/house spray first. If you think that's not worked, you can also use the cats flea treatments which will also affect lice and mites (I believe). After my horrendous broody red mite experience, I've dosed any sitting hens with Frontline at the beginning - just drop it onto the back of their necks where they can't get to it when preening. But you do have to steer clear of their eggs for a while (two weeks? can't remember) so OK for a broody but not for normal laying hens.
H