Several parts combine into one character.

Traditional 號: a mouth shouting (口) combined with a tiger (虎) — "to roar like a tiger / to call out loudly". The character generalized from "loud cry" to "name / signal / number / title". Three forms: 繁體 號 / 新字体 号 / 简体 号 — Japan and Mainland China both adopted the simpler 号, dropping the tiger entirely.

号 anchors a wide vocabulary across CJK: identification numbers, signals, dynasty era-names, and ordinal day markers.

Mandarin: hào, falling 4th tone (simplified 号). 号码 (hàomǎ, number / code), 信号 (xìnhào, signal — traffic light, electrical signal, etc.), 学号 (xuéhào, student ID), 房号 (fánghào, room number). Also a critical Mandarin date marker: 几月几号? (Jǐ yuè jǐ hào? "What's the date?") — Mandarin uses 号 for day-of-month in casual speech (formal writing uses 日). 五月五号 = May 5.

Japanese: on-reading ゴウ (gō) for compounds — 番号 (bangō, number), 信号 (shingō, traffic signal — every Japanese road safety lesson), 暗号 (angō, code / cipher), 年号 (nengō, era name — Japan's system of naming each emperor's reign: 平成 Heisei, 令和 Reiwa, etc., is one of the world's last continuous era-naming traditions), 一号 (ichigō, first issue / model 1). The 年号 system is one of the most distinctive features of Japanese culture — every Japanese document includes both Western year and 年号 designation.

The Japanese magazine industry uses 号 to count issues — 9月号 (kugatsugō, September issue), 創刊号 (sōkangō, inaugural issue). The character carries publishing weight.

Memory aid: a roaring tiger's call → an identifying number or name.