Who investigates a signature that has been copied to another document?

The investigation of a copied signature typically falls under the jurisdiction of forensic document examiners, who specialize in analyzing handwriting and signatures. They may work in conjunction with law enforcement agencies or legal professionals if the matter involves potential fraud or forgery. Additionally, the context of the document—such as whether it's related to a legal case or financial transaction—will influence the specific authorities or experts involved in the investigation.