Summary：
1. Causing of the mistakes: The tone of speech is sometimes too strong on the restricting and compelling public signs. Target readers can understand them without problem, but may feel uncomfortable. Changes should be made to the expressions on such signs in order to make them more friendly and politely.
2. Ways of avoiding such mistakes:
1) Avoid using too many “no” on signs, which is a definitely negative word. It can be replaced by a good deal of other expressions, such as “hand