Do you know what pinfeathers look like? Pinfeathers can sometimes look a bit like ingrown hairs. You should not pluck out pinfeathers, because they are the normal early stage of growing new feathers.
Have you tried looking very closely at some of your other chickens? If they all have the same things, and do not seem bothered, then the things are probably normal (even if you never noticed them before.)
I do not know what the little black things are, which is why I am offering somewhat general suggestions of what else to try looking for or looking at.