What does yellow lettering inside a yellow rectangle with a black background identify?

The presence of yellow lettering inside a yellow rectangle with a black background specifically indicates a taxiway location sign. This type of sign is utilized to provide pilots with information regarding their location on the airport's taxiway system. The yellow background is standard for taxiway signs, contrasting with the black text, which enhances visibility and clarity for pilots navigating the airport environment.

Taxiway location signs are vital for situational awareness, particularly in busy airports like O'Hare, where understanding one’s position on the extensive taxiway network is crucial for safe operations. This specific design helps differentiate taxiway information from other signage, such as directional and hold position signs, which have different color schemes and formats to convey distinct instructions or information.