A surname followed by Mr. means to address Mr. so-and-so. For example, "sir Li" means "Mr. Li". In addition, this expression often appears in some Hong Kong films. At this time, it means police officer XXX, for example, "sir Li" means "police officer Li".

Mr. Wang is a kind of respect for men, and is often used to address senior people or male customers in the service industry. Is a countable noun, often used in singular form. Sir can't be used with last name, but it can be used before first name or before first name and last name.