What type of sign is a blue square?

Answer: C — Guide signs for services like rest areas and gas stations

A blue square sign is specifically designated as a guide sign that provides information about services available to drivers, such as rest areas, gas stations, hospitals, and hotels. These signs are crucial for assisting drivers in finding necessary amenities along their routes, especially in unfamiliar areas. The blue color is universally recognized for denoting services, making it easy for motorists to identify them quickly and plan their stops accordingly.