My parents never noticed anything either (but my parents were not neglectful, so I'm sorry if this isn't helpful), though now that they know about what we went through, they look back and see signs - from me and from the people who hurt us. Part of it, for them, is that they never thought people they considered friends would be capable of such brutality toward a child, so I guess people see what they want to see. Also, because of the DID, it was hard for them to see anything amiss because there is an alter whose job it was to appear "normal" so no one would suspect abuse and it would keep others safe.
I am sorry your parents were so oblivious and/or turned a blind eye. I can imagine that hurts a lot. :(