In business situations, use formal titles unless the people you meet tell you otherwise. To get someone's attention you can say: "Excuse me, Sir" or "Pardon me, Madam/Ma'am." To greet someone you can say: "Hello Sir" or "Good morning, Madam/Ma'am."
在商业场合，除非对方告诉你不需要用敬语，否则就得用正式称呼。当要引起别人注意时可以说"Excuse me, Sir"或者"Pardon me, Madam/Ma'am."；在同别人打招呼时可以说"Hello Sir"或者"Good morning, Madam/Ma'am."
Here are the formal titles English speakers use:
1. Sir (adult male of any age)
Sir（任何年纪的成年男性）
2. Ma'am (adult female - North American)
Ma'am（成年女性——常用于北美）
3. Madam (adult female)
Ma'am（成年女性）
4. Mr + last name (any man)
Mr + 姓（任何男士）
5. Mrs + last name (married woman who uses her husband's last name)
Mrs + 姓（用丈夫姓的已婚女性）
6. Ms + last name (married or unmarried woman; common in business)
Ms + 姓（已婚、未婚女性皆可，常用于商业场合）
7. Miss + last name (unmarried woman)
Miss + 姓（未婚女性）
8. Dr + last name (some doctors go by Dr + first name)
Dr + 姓（也有一些医生是用“Dr + 名”称呼的）
9. Professor + last name (in a university setting)
Professor + 姓（用在大学里）
补充：
The phrase "Yes, Sir!" (or "Yes, Madam/Ma'am!") is sometimes used by native speakers in a sarcastic way. For example when a young child tells his father to "close his newspaper" the parent might say, "Yes, sir!" and laugh. You might also hear a mother saying, "No Madam/Ma'am" to her daughter's request for something unreasonable.
"Yes, Sir!"和"Yes, Madam/Ma'am!"这两个表达有时会被英语国家的人用来表达讽刺的意味。比如一个小孩叫他父亲不要看报了，父亲也许会说"Yes, sir!"，然后大笑。你也可以听到母亲对提出无理要求的女儿说"No Madam/Ma'am"。