What characterizes a sign used for runway and taxiway identification?

The characteristic of a sign used for runway and taxiway identification is its black background with yellow inscription. This color scheme is standardized and easily recognizable, ensuring that pilots can quickly identify critical information while operating on the airport surface. The yellow text stands out against the black background, providing high visibility in various lighting conditions, which is essential for safety during taxiing and takeoff.

Other choices suggest features that are not typically used for runway and taxiway identification. Brightly colored signs with graphics might be suitable for other types of information or guidance, but not for airfield identification. Green backgrounds with white inscriptions are commonly used for general guidance signs, such as taxiway direction signs, not for runway identification. Reflective materials are relevant for enhancing visibility, but the critical defining feature of taxiway and runway identification signs is the specific color combination of black and yellow.