"The term 'emoticons'—short for 'emotion icons'—refers to graphic signs, such as the smiley face, that often accompany computer-mediated textual communication. They are most often characterized as iconic indicators of emotion, conveyed through a communication channel that is parallel to the linguistic one. In this article, it is argued that this conception of emoticons fails to account for some of their important uses. We present a brief outline of speech act theory and use it to provide a complementary account of emoticons, according to which they also function as indicators of illocutionary force. More broadly, we identify and illustrate three ways in which emoticons function: 1) as emotion indicators, mapped directly onto facial expression; 2) as indicators of non-emotional meanings, mapped conventionally onto facial expressions, and 3) as illocutionary force indicators that do not map conventionally onto a facial expression. In concluding, we draw parallels between emoticons and utterance-final punctuation marks, and show how our discussion of emoticons bears upon the broader question of the bounds between linguistic and non-linguistic communication."
(Eli Dresner and Susan C. Herring, 2010)
Dresner, E., & Herring, S. C. (2010). "Functions of the non-verbal in CMC: Emoticons and illocutionary force". Communication Theory, vol. 20, no. 3, pp. 249-268.
http://ella.slis.indiana.edu/~herring/emoticons.pdf