What color scheme indicates enforceable speed limit signs?

The choice with a white background and black letters indicates enforceable speed limit signs because this color scheme aligns with the guidelines established by the Manual on Uniform Traffic Control Devices (MUTCD). This manual provides standardization for street signs across the United States, ensuring consistency and clarity for drivers.

Enforceable speed limit signs are meant to inform drivers of the legal speed limits on roadways, making it crucial that they are easily readable from a distance. The high contrast of black letters against a white background enhances visibility under various lighting conditions, which is essential for safety.

Other color schemes mentioned are used for different types of signs. Yellow backgrounds usually signify warning signs, conveying caution without enforceability. Red backgrounds are typically used for stop signs or prohibition signs, marking areas where certain actions are impermissible, rather than setting speed limits. Green backgrounds usually indicate directional information or guidance, rather than enforceable regulations like speed limits. Thus, the white-on-black color scheme is specifically designated for signs that convey enforceable regulations, such as speed limits.