As per usual, and especially true in the US, the story is complicated. There was no law on the books that prevented women from signing mortgages in the 60s, but there was systematic discrimination and discounting or ignoring a woman's ability to make good on a loan.
> Part I discusses the extent of discrimination against women in this field. It concluded that such discrimination is wide-spread and takes two forms. First, lenders discount a working wife's income when she applies with her husband for a home mortgage. Second, lenders are less likely to make a loan to a single woman than to a man.
you still have not addressed the claim that "women could not sign mortgages in the 70s"