Which type of sign would inform pilots about applicable radio frequencies?

The correct answer is the type of sign that provides information pertinent to pilots about applicable radio frequencies. Information signs are designed specifically to convey important data that can aid in the navigation and communication processes for pilots. This includes details about radio frequencies that are necessary for coordinating with air traffic control, communicating with other aircraft, and receiving pertinent updates while in flight operations.

Information signs are distinct from other types of signs, such as location signs, which indicate specific locations and help with ground navigation, or designation signs, which mark runways and taxiways. Runway Distance Remaining signs indicate the distance a pilot has remaining until reaching the end of the runway but do not provide frequency information. Thus, the role of information signs is crucial for ensuring pilots have the most relevant and up-to-date communication capabilities, making this the correct choice in this context.