I'm sorry, I don't understand. Well, I agree that it would be perjury. But then there would be no proof of perjury, and the perjurer would get away. That can't offer much assurance to the person accepting a signature.

Besides, the argument applies to other signs of consent, like verbal consent. Suppose you give a verbal consent to an agreement and then renege. The other party drags you to court. The judge says, "Did you verbally consent to this contract?" Saying "no" likewise would be perjury.