13 GCA § 3406
Negligence Contributing to Alteration or Unauthorized
View official PDF ↗Signature. Any person who by his negligence substantially contributes to a material alteration of the instrument or to the making of an unauthorized signature is precluded from asserting the alteration or lack of authority against a holder in due course or against a drawee or other payor who pays the instrument in good faith and in accordance with the reasonable commercial standards of the drawee's or payor's business.
Reconstructed from the Guam Code Annotated. For the authoritative version, see the official PDF.