Any advertising sign which violates the provisions of this chapter or the rules adopted by the director is hereby declared to be illegal. The director shall give thirty days’ notice, by certified mail, to the owner thereof to remove the same if it is a prohibited sign, or cause it to conform to rules promulgated by the director if it is an authorized sign. If the owner fails to act within thirty days as required in the notice, or if the director is unable to ascertain the ownership of the sign, then such sign must be deemed abandoned and the director may remove such sign, and to this end the director may enter upon private property for the purpose of removing such sign without liability for the director’s actions.