For the Purposes of this Act, the Signature of the Convener or of the Preses of a Meeting of Commissioners of Supply adhibited to any Paper or Document shall be equivalent to the Signatures of the whole Commissioners of Supply present, at a Meeting thereof; and the Signature of the Lord Provost, or Provost, or Chief Magistrate of the Burgh, or of the Preses of a Meeting of the Magistrates of the Burgh, adhibited to any Paper or Document, shall be equivalent to the Signatures of the whole Magistrates present at such Meeting; and the Addition to such Signatures respectively of the Words " Convener," " Lord Provost," " Provost," " Chief Magistrate," or " Preses," shall be good primâ facie Evidence that such Signature is the Signature of such " Convener," " Lord Provost," " Provost," " Chief Magistrate," or " Preses," as the Case may be, and that such Paper or Document is genuine and authentic.