If my parents had forbidden ASL or any types of sign language in the house -- I doubt sis and I would be there long!
But thankfully, Mum was motivated and determined enough to improve her signing skills and ensured that sis and I had the best sort of education possible and accommodating our needs.
Dad signed, yes, but not much...still it was adequate enough for us..didn't bother us because we used TC as well -- Total Communication: verbal and sign at the same time.