Where any advertisement has been erected, exhibited, fixed or retained Presumption in case

upon or over any land, building, wall, hoarding, frame, post. kiosk, structure, of contravention. vehicle, neon sign or sky-sign or displayed to public street or public place in contravention of the provisions of this Act or the regulations made there under it shall be presumed, unless the contrary is proved, that the contravention has been made by the person or persons on whose behalf the advertisement purports to be or the agents of such person or persons.