15. Where it is required to be proved for the purposes of this Act that any person has been convicted of an offence specified in the Schedule to this Act or has been disqualified by an order of a Court for holding a licence, such conviction or order may be proved, in addition to any other mode provided by any law for the time being in force-(a) by an extract certified under the signature of the officer having the custody of the records of the Court in which such conviction was had, or such order was passed, to be a copy of the sentence or order, or(b) in the case of a conviction, by a certificate signed by the officer in charge of the jail, in which the punishment or any part thereof was undergone, or by the production of the warrant of commitment under which the punishment was suffered, together with, in each of such cases, evidence as to the identity of the person so convicted or in respect of whom such order was passed.