A semaphore signal is a method used in communication to convey information through visual signals. It typically involves the use of flags, lights, or mechanical arms that can be positioned in different ways to represent specific messages. Semaphore systems are often used in maritime contexts, where ships use flags to communicate with each other over long distances. In computing, semaphore signals are a synchronization mechanism used in programming to manage access to shared resources. They help prevent conflicts when multiple processes or threads attempt to access the same resource simultaneously, ensuring that operations are performed safely and efficiently. This concept is crucial in operating systems and concurrent programming.