What is the appearance of direction signs?

The appearance of direction signs, specifically in the context of O'Hare Airport and similar facilities, is characterized by a black arrow on a yellow background. This color scheme is specifically designed to enhance visibility and clarity, ensuring that drivers can easily identify the direction they should proceed in. The distinctive combination of black and yellow is widely recognized for conveying information efficiently, as yellow typically denotes caution or alertness, while black arrows provide straightforward guidance on movement direction.

In contrast, other color combinations such as red with white or blue with white are generally used for different types of signage, such as warnings or informational signs, which do not specifically indicate travel direction. Yellow with black X's would typically signify a stop or hazard, rather than provide navigational guidance. Thus, the choice of a black arrow on a yellow background aligns with established standards for directional signage, making it the correct answer in this context.