“When a local government enacts a sign regulation, it is likely that
some existing signs will not conform to the new regulations. Local
sign regulations should address existing signs, particularly those that
do not conform to newly enacted regulations. A lawfully existing sign
that does not conform to new sign regulation may be treated as a prior
nonconforming use, and allowed to remain provided it is not altered.
Alternately, the municipality may attempt to have them removed.”