信号
しんごう · shingou · JLPT N3 · noun
traffic light
🚦 信号 = message (信) + sign (号): a sign that sends a message
信 means trust or message (as in 通信, communication) and 号 means sign or number (as in 番号). Together: a sign carrying a message, hence signal, and in daily speech the traffic light. Sound hook: shingou tells you when the thing can go.
信 — person 亻 + speech 言
信 combines 亻(person) with 言(speech), depicting a person standing by their words. The original sense is 'truthfulness' or 'sincerity'—what a person says can be trusted. From this it extended to 'believe,' 'trust,' and later 'message' or 'letter,' since a letter carries one's word.
号 — mouth 口 + tiger 虎
Originally written 號, combining 口 (mouth, indicating a cry or call) with 虎 (tiger) as the phonetic and a hint at a loud roar. It first meant to shout or call out, then extended to a name, title, or signal. The simplified form 号 keeps only the upper element.