Guerrilla proofreading means marking up a public sign to correct or point out a grammatical error or typo. Guerrilla proofreading does seem to be a popular hobby for some people. They can get quite agitated about apostrophes, invisible hyphens, misspelled words and other such entities. People who enjoy guerrilla proofreading are called guerrilla proofreaders. (Source: Word spy)

Guerrilla proofreading指把一些公共指示牌标记下来以纠正或指出其中的语法或拼写错误，我们可称之为“公众纠错”。有些人的确很喜欢做这种“公众纠错”。他们看到省略单撇号、未显示的连字符、拼错的单词等这一类错误时就会很生气。喜欢做“公众纠错”的人就被称为“公众纠错师”。

For example:

Tony is a college English teacher, and he really enjoys so-called guerrilla proofreading in his spare time. Whenever he sees something wrong on a public sign, he would mark it down and write to the government to complain about it.

托尼是一位大学英语老师，他很喜欢在业余时间做所谓的“公众纠错”。只要他看到公共指示牌上有错，他就会记下来然后写信到政府部门进行投诉。