Final answer:
An interstate route sign with an odd number indicates a north-south oriented highway in the U.S. Interstate Highway System, with numbers increasing from west to east.
Step-by-step explanation:
An interstate route sign ending in an odd number generally indicates that the highway is primarily north-south in orientation. In the United States Interstate Highway System, odd-numbered routes increase in number from west to east across the country. For example, I-5 runs along the west coast, while I-95 traverses the east coast. These route numbers also suggest that the road they are marking is part of the larger national network of interstate highways. Additionally, these signs may include other information such as the direction the route is heading, which can be particularly useful for travelers and commuters.