(1) Unless specifically denied in the pleadings, each signature on a security certificate or in a necessary indorsement is admitted;

(2) If the effectiveness of a signature is put in issue, the burden of establishing effectiveness is on the party claiming under the signature, but the signature is presumed to be genuine or authorized;

(3) If signatures on a security certificate are admitted or established, production of the certificate entitles a holder to recover on it unless the defendant establishes a defense or a defect going to the validity of the security; and

(4) If it is shown that a defense or defect exists, the plaintiff has the burden of establishing that the plaintiff or some person under whom the plaintiff claims is a person against whom the defense or defect cannot be asserted.