Usually you can see in China, some buses, banks, hospitals and other service outlets have a sign attached to them, reading 青年文明号, that is quite beyond me. Especially the word 号 what does it mean here? Is it something like the name of a ship or an aeroplane?
号 is a common designation word for naming man-made vehicles like ships, planes and trains.
Ronald Reagan = 罗纳德·里根
USS Ronald Reagan = 罗纳德·里根号 (super-carrier named after Ronald Reagan)
“青年文明号" is a youth organization that emphasize on "Youth movement " And the word 号 in the organization's name signified this fact.
It is in fact, comparing itself to a ship or train (Something that move purposefully ; a vehicle for advancing development )
號 in the sense of verb is "calling". 號 in the sense of noun is the words that is used in "calling".
In specific context, 號 is a name allowing others to call someone or something. You can find this context in 名號, 稱號, 號稱 and 字號. 號數 is a number allowing others to call someone or something.
In imperial China, ships are not named. In Western world, ships are named. When China imports those big iron ships, Chinese also named it. But people at that time called it like 新華輪, where 輪 is 輪船 (wheel-ship) and 輪船 is extended to more advanced ships without wheels. It is no 號 at the end of name.
The use of suffix on ships probably comes from Japan. Japanese enforced all the names of non-government ships to append 丸 as suffix. When Chinese writers translate these ship names, every 丸 is simply translated to 號. This practice becomes the suffix of ship names.
In the eyes of Chinese, those big iron ships have implicit meaning the "advanced". Yes, 青年文明號 is like ship name, it is an implicit use of ship name. 青年文明號 is a youth organisation under Communist Party. This kind of metaphors are common in the party's language.
Unlike other answers I always interpret the 号 as trumpet, since natural trumpet is heavily connected to the Party, from the warfare assault in WWII to nowadays school ringings. Never mind since no matter what does 号 mean 青年文明号 always mean an appeal to civilization, and sometimes an local organisation for that. I firmly believe that different people who use the term define 号 with different meanings, one of the two, but it just doesn't matter.