A call sign is a unique identifier used in communication, especially in aviation, military, and amateur radio. It helps to distinguish between different operators or units, ensuring clear and efficient communication. For example, a pilot might use a call sign like “Skyhawk 123” to identify their aircraft during radio transmissions. Call signs can also be used in various organizations, such as the United States military, where they often reflect the unit's name or mission. In amateur radio, operators choose their own call signs, which can be a combination of letters and numbers, making it easier to connect with others in the hobby.