Subject to the provisions of this Act, if a signature on a bill is forged or placed thereon without the authority of the person whose signature it purports to be, the forged or unauthorized signature is wholly inoperative, and no right to retain the bill or to give a discharge therefor or to enforce payment thereof against any party thereto can be acquired through or under that signature, unless the party against whom it is sought to retain or enforce payment of the bill is precluded from setting up the forgery or want of authority: Provided that nothing in this section contained shall affect the ratification of an unauthorized signature not amounting to forgery.