回顾以前贴的论文, 发现少了文献综述部分. 多谢网友提醒, 现在粘上.
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2. Rationale
2.1. Differentiating of signs and public signs
2.1.1. Sign
Basically, a sign is “a piece of paper, metal etc in a public place, with words or
drawings on it that give people information, warn them not to do something.” (Longman Dictionary of Contemporary English, 2005).
      From this definition we can see that sign can be either picture or word alone, or the combination of pictures and words.
      C.S. Pierce define