2.2 Categories of public signs
According to Chinese-English Translation of Public Signs written by Lv Hefa, public signs can be classified into four types: directive public signs, warning public signs, limiting public signs and forcing public signs.
2.2.1 Directive public signs
Some public signs convey instant information and offer directive service to those in need. They help the public know surroundings well. For example, the letter “P” at the entrance of a supermarket or a street means “parking”. In other words, it’s a place where you can park your vehicles. Besides, the word “Metro” with an arrow indicates the entrance of subway station for you.
2.2.2 Warning public signs
Generally speaking, warning public signs convey warm and kind notices for the public. Sometimes they remind people of something unnoticed, like “Wet Paint（油漆未干）”, “Sold out（售罄）”, “Fully booked（订满）”. Sometimes they call people’s attention to the dangers before them. In public places, we often see the signs like “Mind the gap（注意站台间的空隙）” or “Please watch your steps（小心台阶）”.
2.2.3 Limiting public signs  
Limiting public signs refer to restrictions on people’s behaviors or the target readers. For example, “For emergency use only（紧急使用）” makes a regulation on the use of urgent passage. And “Keep Right（靠右行驶）” requires all vehicles to drive only on the right of the road. Similarly, “Staff Only（闲人免进）” is seen on the door of office room, meaning that no one except for staff or employees can go in.
2.2.4 Forcing public signs
Forcing public signs make a mandatory provision in a strong tone. In most cases, those forcing public signs are carried out under coercion by government. If someone violates the rules, he may receive punishment from related departments. The familiar public sign “No Smoking（禁止吸烟）” makes a mandatory order that smoking is prohibited in that place.

3. The translation strategies of public signs
3.1 Translation theories and principles
Viewing the translation theories of western and Chinese translators throughout history, this paper studies translation theories and principles of public signs from three perspectives.
3.1.1 Communicative translation
Newmark divided texts into three types: expressive text, informative text and vocative text (Communicative and Semantic Translation). Besides, Newmark also brought forward semantic translation and communicative translation for different texts. Expressive text should follow semantic translation while vocative text should use communicative translation.
It’s obvious that public signs belong to vocative text, because they aim to provide directive and commentary information. Communicative translation means that it can accurately convey the contextual meaning of original text and make the content acceptable and comprehensible to readers. In the translation of public signs, the language characteristics of Chinese public signs just need to be regarded as reference, translators should focus on the content that need to be transmitted to English readers.
3.1.2 Avoid the influences of negative transfer of mother tongue
Disparities of thinking models and language expression between English and Chinese are huge. Translating with a thinking model of native language will lead to the so-called Chinglish. Public sign should be reader-oriented and translated in accordance with English language consciousness, communicative habits and cognitive mode.
3.1.3 Three principles of translations of public sign
Based on Newmark’s divisions of texts and characteristics of public signs translation, the paper concludes three translation principles for translations of public signs. They are principles of consistency, conciseness and comprehensibility. 城市公示语英译现状及对策研究英文论文(3):http://www.751com.cn/yingyu/lunwen_452.html