Tex. Rev. Civ. Stat. art. 4012
Any veteran of any of the wars mentioned in this title, their wives, widows or members of their families, and any minister of religion, or any fireman, sister of charity or member of any religious society of like character, who desires to receive the benefits of free or reduced transportation as mentioned in this title shall present to the president, manager, officer, or person authorized to issue such transportation satisfactory evidence that he or she is entitled thereto, as herein provided. The officers entitled to the benefits of this law shall, when presenting themselves to the agent of any such railway or interurban railway company for the purchase of a ticket or to pay his fare, exhibit to such agent in case of the Adjutant General and State Rangers a certificate of the Secretary of State under the state seal, in case of sheriffs and constables and their deputies a certificate under seal of the county judge of the county where they hold office and in case of officers of a city or town a certificate under seal of the mayor of such city or town stating that such person is entitled to the reduced fare herein provided for. Sheriffs and constables shall designate in writing the two deputies entitled to the reduced rates herein provided for. If the sheriff or constable has designated two deputies who are entitled to such reduced rates, then no deputy of such sheriff or constable shall be entitled to free transportation under the provisions of the pass laws of this State.
Tex. Rev. Civ. Stat. Ann. art. 4012