This is the fifth in a series of posts where I'm looking at how the Chinese view numbers, often from a superstitious basis.
The Chinese character for four (Sì) is shown on the right hand side of the main image above.
Four is universally regarded as a bad number in Chinese culture. Once again, that's because it sounds like other words.
In particular, four sounds like 死 (Sǐ) which means "death". It's similar in Cantonese where the word is sei, it's the same issue. It's considered an unlucky number because of this.
You'll find buildings in Asia that don't have a floor 4 (similar to how many Western buildings years ago had no floor 13). Some buildings take it even further and have no floor 4, 14, 24, 34, and so on.
Four is so frowned upon that people avoid saying it, and don't display it anywhere. People will get upset if they're issued an ID or credit card that has the number 4 in it.