Final answer:
Texas state highways are marked with a blue and red shield, which serves as a clear and distinct navigational marker for drivers on Texas roads.
Step-by-step explanation:
Texas state highways are indicated with a blue and red shield. This symbol is a way for drivers to easily recognize the route markers for state highways when navigating roads in Texas. The symbol for Texas state highways is distinctive from other markers such as the pentagon shape or the Texas silhouette, providing a clear guide for travelers in the state.