I use it all the time. This is a sad face. It portrays an emotion of mild discomfort. In c-space, they call this an emoticon. This is the famous 'grin' emoticon.
Abbreviations are very popular in E-mail epistles.
BTW, the writer's opinion is often not humble at all. Unfortunately, in c-space just like any other community, you will come across some people who act as jerks. As tempting as it may be, please don't respond to them with flaming E-mail. Emoticons Netiquette Home Page . . . . This is the ninth of a series of elementary articles designed for surfing the Internet.