Any sign legally existing on the effective date of this Subchapter that does not conform to use, location, height or size with the regulations of the zone in which the sign is located, will be considered a legal nonconforming use or structure and may continue in such status until it is either abandoned or removed by the owner. If the sign is damaged to the degree that it requires removal or becomes dilapidated, it shall be replaced with a sign that complies with the provisions of this Subchapter.
Okla. Admin. Code § 120:10-15-14