Just as an exclamation mark will denote excitement, a smiley emoticon denotes humor.
From the evangelicaloutpost.com
I also image a frowny-face emoticon belongs at the end of the last sentence.
From the scienceblogs.com
More examples
A representation of a facial expression (as a smile or frown) created by typing a sequence of characters in sending email; ":-( and :-) are emoticons"
An emoticon is a textual expression representing the face of a writer's mood or facial expression. Emoticons are often used to alert a responder to the tenor or temper of a statement, and can change and improve interpretation of plain text. ...
(Emoticons (Ben & Jason album)) Ben & Jason were a singer-songwriter duo from London consisting of Ben Parker and Jason Hazeley. Formed in 1998 and pre-empting the so-called New Acoustic Movement by about a year, they released three albums on Go! ...
A graphical representation, either in the form of an image or made up of ASCII characters, of a particular emotion of the writer
(Emoticons) These are the sideways smiles and frowns used in email to indicate emotions, e.g. :-) would indicate a smile and :-( would indicate a frown!
Emoticons are symbols used in place of verbal or visual communication cues to help convey the tone or emotion of the e-mail message. They are made by a combination of keyboard keys. Some common emoticons are:
(Emoticons) Combinations of keyboard characters that express emotion. For example, happy :-); sad :-(.
(Emoticons (emotions + icons)) are yet another type of Internet slang. These simple keyboard pictographs can pepper text to indicate intonation so that a joke, for example, will be understood as such. ...
(Emoticons) A series of keyed characters used especially in e-mail to indicate an emotion, such as pleasure [:-)] or sadness [:-(].