Any bonds hereafter executed and delivered by any city of the first class may be countersigned and attested by a facsimile signature of its City Controller in lieu of his manual signature and a facsimile of the seal of the city may be imprinted or otherwise reproduced on said bonds in lieu of the manual seal of the city: Provided, That such bonds shall be signed by the fiscal agent of the said city by the manual signatures of two of its duly authorized officers.