“小姐 means prostitute" isn't mandarin.It is slang. 这个情况是这样形成的。在公共场所，皮条客们来跟你搭讪的时候是不会直接说“先生，你想要个妓女吗？”的。我不知道在外国是怎样的，在中国这样说太直露了。所以他们会说“先生，你想要个小姐吗？”说到“小姐”这个词的时候用一种暧昧的语气。于是你就知道他暗示的是什么了。 时间长了，“小姐”就渐渐地成了妓女的代名词。 个人感觉，在中国人的口语中，指young ladies 的“小姐”和指prostitute的“小姐”是可以听出来的。指young ladies 的“小姐”在句子中会轻读。而指prostitute的“小姐”会重读。尤其是“小”字会特别加重音，还会略微拖长。因此不难分辨。当然，这也有可能只是我所生活的地方的口音。

"小姐" in Chinese has three basic meanings: 1) A title of respect prefixed to a woman's name or position, like Miss, Ms 2) A young lady. 3) Slang: A prostitute I don't know about Hong Kong or Taiwan. But in China Mainland, young ladies would feel good if you add her surname before "小姐", for example, “王小姐” (Ms Wang). Or, if you don't know her name, you could add "这位" (this) before "小姐", for example, "这位小姐" (My lady). All these additions just help.

No, it depends in different sentences. You can call young lady 小姐.

Not all over the Mainland. In the north. Beijing for example. So you're pretty safe in Guangdong or Shanghai.

I thought that's what you call waitresses? :P