(a) The requirements of this subchapter do not apply to a sign that was erected in violation of local ordinances, laws, or regulations applicable at the time of its erection.
(b) The requirements of this subchapter do not apply to a sign that, having been permitted to remain in place as a nonconforming use, is required to be removed by a municipality because the sign, or a substantial part of it, is blown down or otherwise destroyed or dismantled for any purpose other than maintenance operations or for changing the letters, symbols, or other matter on the sign.
(c) For purposes of Subsection (b), a sign or substantial part of it is considered to have been destroyed only if the cost of repairing the sign is more than 60 percent of the cost of erecting a new sign of the same type at the same location.
(d) This subchapter does not limit or restrict the compensation provisions of the highway beautification provisions contained in Chapter 391, Transportation Code.