Here is how I read it. In (c) it describes the physical appearance and location of the sign. (b) just says that everything in (c) applies except for needing the 51 on it. and (c) talks about 51 because (a) deals with bars, etc.. Basically you have to read a, b and c to see how they relate to each other.
a) A business that has a permit or license issued under Chapter 25, 28,
32, 69, or 74, Alcoholic Beverage Code, and that derives 51 percent
or more of its income from the sale of alcoholic beverages for
on-premises consumption as determined by the Texas Alcoholic
Beverage Commission under Section 104.06, Alcoholic Beverage Code,
shall prominently display at each entrance to the business premises
a sign that complies with the requirements of Subsection (c).
(b) A hospital licensed under Chapter 241, Health and Safety
Code, or a nursing home licensed under Chapter 242, Health and
Safety Code, shall prominently display at each entrance to the
hospital or nursing home, as appropriate, a sign that complies with
the requirements of Subsection (c) other than the requirement that
the sign include on its face the number "51".
(c) The sign required under Subsections (a) and (b) must
give notice in both English and Spanish that it is unlawful for a
person licensed under this subchapter to carry a handgun on the
premises. The sign must appear in contrasting colors with block
letters at least one inch in height and must include on its face the
number "51" printed in solid red at least five inches in height.
The sign shall be displayed in a conspicuous manner clearly visible
to the public.