A sign that was lawfully erected prior to January 13, 2000 but which does not conform to one or more aspects of the requirements of this chapter, may remain in use subject to the requirements of this section and other applicable requirements of LDO Chapters, with the exception of nonconforming pole signs or billboards. Further, any nonconforming sign or any new sign that is part of a Master Sign Plan (formerly known as a Uniform Sign Plan) within a Planned Development may be installed, replaced, maintained and repaired provided that the Master Sign Plan was approved prior to January 13, 2000, and the sign is installed in accordance with the Master Sign Plan or in accordance with Chapter 9, whichever is applicable.