Which airline uses the call sign "American"?

The call sign "American" is specifically associated with American Airlines. Airlines often use call signs as a way to identify themselves during communications, especially in air traffic control and amongst pilots. American Airlines has historically used the call sign "American" in various operations. This call sign is recognized internationally and is part of the airline's brand identity.

While Delta Airlines and United Airlines have their own distinct call signs, they do not use "American." Republic Airways, which operates regional flights for various major airlines, also has its own call sign distinct from American Airlines. Thus, the association of the call sign "American" exclusively with American Airlines makes it the correct answer.