(1) Unless specifically denied in the pleadings each signature on an
instrument is admitted. When the effectiveness of a signature is put in
issue
(a) the burden of establishing it is on the party claiming under
the signature; but
(b) the signature is presumed to be genuine or authorized except
where the action is to enforce the obligation of a purported
signer who has died or become incompetent before proof is
required.
(2) When signatures are admitted or established, production of the
instrument entitles a holder to recover on it unless the defendant
establishes a defense.
(3) After it is shown that a defense exists a person claiming the
rights of a holder in due course has the burden of establishing that he
or some person under whom he claims is in all respects a holder in due
course.