Any signs existing at the time of the passage of this chapter and
which violate any provisions thereof shall be deemed a nonconforming
use and may be continued, maintained and repaired upon the present
premises or location; provided, however, that such sign was lawful
under any prior ordinance. Any nonconforming sign which is associated
with a change in occupancy or ownership shall necessitate an application
to the approving authority. Any sign unlawful under any prior ordinance
shall remain unlawful unless it complies with the provisions of this
chapter and there is issued by the Zoning Officer a sign-erection
permit therefor.