Emoticon

An emoticon is a combination of punctuation marks and other symbols used in text messages and email to indicate emotions. The best known (and original) emoticon is the "smiley", which consists of a colon and a close-parenthesis (sometimes also written with a dash) thus :) or :-) . These combinations represent a smiling face turned sideways. A large number of emoticons have been devised using similar structure.

Sheldon describes his happiness at supposedly finding evidence of magnetic monopoles on the Arctic expedition during the summer of 2009 by saying he is like a "colon-capital-D" which is :D . When he is informed that his data had been tampered with, his expression changes to shock, which Raj describes as "colon-capital-O", or :O .