Why is the official website of China's high-speed rail system called 12306? The URL is literally 12306.cn/ . Is it a pun? Transliteration? Company registration number? Postal code of their headquarters?
The obvious answer that doesn't explain anything is "they couldn't use Chinese characters at the time so they did this instead". There are other companies that use a number for ASCII name, each for their own reasons, so why this number in particular for the railway?
My Chinese-speaking person at hand has no clue. ๐