P.R. Laws tit. 19, § 608
(a) Except when the authenticity of, and authority to make, a signature on the instrument is denied in the pleadings, in a judicial action with respect to the instrument, the authenticity and the signature will be construed as admitted. If the validity of a signature is denied, the burden of establishing validity is on the person claiming it, but the signature is presumed to be authentic if the action is not to enforce the liability of a purported signer who is dead or incompetent when evidence of validity of the signature is required. If an action to enforce the instrument is brought against a person as the undisclosed principal of a person who signed the instrument as a party to the instrument, the plaintiff has the burden of establishing that the defendant is liable on the instrument as a represented person under § 652(a) of this title.
(b) If the validity of signatures is admitted or proved and there is compliance with subsection (a) of this section, a plaintiff producing the instrument is entitled to payment if the plaintiff proves entitlement to enforce the instrument under § 601 of this title, unless the defendant proves a defense or claim in recoupment. If a defense or claim in recoupment is proved, the right to payment of the plaintiff is subject to the defense or claim, except to the extent the plaintiff proves that the plaintiff has rights of a holder in due course which are not subject to the defense or claim.
History —Aug. 17, 1995, No. 208, § 2-308; Aug. 31, 1996, No. 176, § 2.