Termination by abandonment. Any nonconforming sign, the use of which is discontinued for a period of 90 days, regardless of any intent to resume or to not abandon such use, shall be deemed to be abandoned and shall not thereafter be reestablished. Any period of such discontinuance caused by government actions, strikes, material shortages or forces of nature, and without any contributing fault by the nonconforming user, shall not be considered in calculating the length of discontinuance for purposes of this subsection.