Any lawful building or other structure, or any lawful use of a building, structure land, or sign legally existing on the effective date of this chapter, or authorized by a building permit issued prior thereto, which does not conform with the provisions of this chapter, unless otherwise specified within this article, shall be considered a lawful nonconforming building, structure, use, or sign and may be continued in the form evident at the time of adoption of this chapter although such use does not conform to the provisions of this chapter except as specified herein.