A sign that would be permitted under this chapter only with a sign permit, but which was in existence on the effective date of this chapter and which was constructed in accordance with the ordinances and other applicable laws in effect on the date of its construction, but which by reason of its size, height, location, design, or construction is not in conformance with the requirements of this chapter, shall be allowed to remain in place and be maintained, provided that no action is taken which increases the degree or extent of the nonconformity. A change in the information on the face of an existing nonconforming sign is allowed; however, any nonconforming sign shall either be eliminated or made to conform to the requirements of this section when any proposed change, repair or maintenance would constitute an expense of 50% or more of the replacement value of the sign.