The word "信号" is formed through a logical, conceptual combination of its two component characters. The first character, "信" (xìn), carries the core idea of a message or information that is to be communicated or trusted. The second character, "号" (hào), contributes the notion of a sign, mark, or audible/visible indicator. By joining them, the compound creates the integrated concept of a "message-sign", that is, a specific sign or physical phenomenon (like a light, sound, or wave) whose sole purpose is to systematically convey information or a message from one point to another.