Emoticons

They're used chiefly to mark the tone of the preceding sentence, or to indicate the writer's feelings about something they have just mentioned.

Emoticons tipically represent a facial expression. The following are some of the more commonly seen:

:-) happy (a 'smiley')

:->> huge smile

:-( unhappy

:-c very unhappy

:-X my lips are sealed

:-Q I don't understand

;-) winking

X= fingers crossed

:-p sticking one's tongue out

:-D laughing

:'-( crying

:-/ sceptical

:-| bored, indiferent

:-O surprised

:-* kiss

O:-) angel (for innocent remarks)

>:-) devil (for devillish remarks)

:-Y aside comment

:-V shouting

<:-) stupid (wearing a dunce's cap)

:-> sarcastic

:-S words fail me

:-@ shocked

((H)) big hug

Source: Oxford Dictionary of English.