A laughing face is an "emoticon" used by Facebook users to add a sense of amusement or humor to a wall post or comment. Emoticons are generally textual faces created by using certain letters and symbols. Although the laughing face emoticon still shows up as merely a combination of these certain letters and symbols when written on a wall, additions to Facebook as of May 2011 allow you to create visual emoticons when you add the laughing face in a message to another member.
Use a colon -- “:” -- to form the eyes of your laughing face.
Add a hyphen -- “-” -- to form the nose for your laughing face: ":-."
Type a capital “D” to make the mouth of your laughing face: ":-D."