Applicability of section. The following regulations shall govern
the erection and alteration of buildings and structures and the use
of land in the Industrial District; except, however, that these regulations
shall not apply to an existing building or structure, nor to the existing
use of any building, structure or land, if such existing building
or structure or existing use of any building, structure or land was
a lawful use under the governing provisions of prior zoning ordinances,
nor to an alteration thereto for a use or for any purpose or in any
manner which is not substantially different from that to which it
was put before alteration, nor to lots shown in a subdivision plat
which has been approved by the Salem Planning Board. However, in the
event of discontinuance of a nonconforming use for whatever reason
for 12 consecutive months, then the following regulations shall govern
the erection and alteration of buildings and structures and the use
of land in the Industrial District. Further, signs of all types and
descriptions must conform to all requirements of this chapter not
later than April 1, 1982.