Any sign which no longer advertises a bona fide business conducted, or a product available for purchase by the public for a period of ninety (90) days or more, shall be taken down and removed by the owner, agent or person having the beneficial use of the building or structure upon which such sign may be found, within thirty (30) days after written notification from the City of Oakdale, and upon failure to comply with such notice within the time specified in such order, the City is hereby authorized to cause removal of such sign, and any expense incident thereto shall be paid by the owner of the building or structure to which such sign is attached, or, if the sign is not attached to a building, by the owner of the sign.