ID number

(mouth/small box radical) + (pirate's hook)
★★★★☆
5 strokes
This is different from the related kanji 番 and  数! 号 doesn't refer to an individual number like 8 or 4. 号 refers to specific identification numbers: phone numbers, zip codes, pin codes for your ATM, etc.

Onyomi

GOU

The apartment's ID number tells you which apartment to GO to.

Mnemonic

The Bizarro Dentist put a number of pirate hooks in your mouth during the Bizarro Checkup.

Kunyomi

( xxx ) ごう a SUFFIX which you put after a numbered item (apartment number, account number, etc.) Like, if you live in room 204, you'd say に ゼロ よん 号。 LAZYSUF
★★★★★

Jukugo

信号(しんごう)

signal ★★★★☆
(believe) + (ID number) = 信号 (signal)

signal, i.e. traffic signal

暗号(あんごう)

a code ★☆☆☆☆
(dark) + (ID number) = 暗号 (a code)

暗証番号(あんしょう ばんごう)

secret code number ★☆☆☆☆
(dark) + (proof) + (number) = 暗証番号 (secret code number)

your secret PIN number you use when you go to the ATM. This is different from a password you use on the internet - that's パスワード。

Synonyms

number
数    数字    号   
sign, symbol, mark
標識    記号    象徴    印    符号    暗号