Presumption as to documents: signatures, execution and custody-origin documents presumed genuine unless effectively rebutted. Section 39 permits four departmental presumptions: handwriting and signatures on specified documents are presumed genuine; documents appearing executed or attested are presumed so unless rebutted; unstamped documents may be admitted for the limited purpose of proving the accused's guilt; and documents recovered from a person's custody are presumed true unless disproved. Authentication under the Foreign Exchange (Authentication of Documents) Rules applies only when a document came from outside India, was received during an investigation of an alleged contravention against the person, and is tendered in proceedings against that person.