Article 204

A private instrument, the signing of which has explicitly been denied by the party against whom it would provide presumptive evidence, does not provide any evidence as long as it has not been proved who made the signature. A statement to the effect that the authenticity of the signature has not been acknowledged shall suffice.

If the party who challenges the authenticity of the private instrument refuses to cooperate in establishing whether it is his signature on the document, the court may draw such inferences as it finds justified in the circumstances.