1) also (sic); used when quoting someone and the person being quoted made a spelling error. This shows that the writer is aware of the mistake but doesn't correct it in order to quote properly.
2) used in chats and forums to point out that someone has made a dumb or disgusting remark. Also used to point out spelling and/or grammar mistakes or annoying txt tlk.
Can be used with or without square brackets.
1) "Your (sic) not aware of this mistake, are you?"