Not wanting to be too graphic, but I think the thread I read mentioned variations in cervixes, and not hips. I guess some women look as though they have given birth? I can't remember which discussion it was, and it doesn't really matter since I don't think it was common. I knew, of course, if you had a c-section, you may have never dilated and so on, but then you would have signs of a surgical birth. Just stuck in my mind since I always thought it was a pretty "either/or" sort of thing, but apparently not always.
I think once someone has given birth that you could tell by the cervix, for my subsequent pregnancies I was told that the cervix is already slightly dilated due to the previous birth but I wouldn't like to swear to it.