At criminal proceedings at which an accused is charged with any offence relating to any seal or stamp used for the purposes of the public revenue or of the post office in any foreign country, a despatch purporting to be from the officer administering the government of such country and transmitting to the State President any stamp, mark or impression and stating it to be a genuine stamp, mark or impression of a die-plate or other instrument provided or made or used by or under the direction of the proper authority of such country for the purpose of denoting stamp duty or postal charge, shall on its mere production at such proceedings be prima facie proof of the facts stated in the despatch.