Is a smiley. The text representation (if you "hover" of over the smiley) is roflblack for some reason.
You must have "smileys" enabled in your profile to see them.
Look below the reply text box to four check boxes.
1) show your signature
2) Automatically parse links
3) Automatically retrieve titles from external links
4) Disable smileys in text
A check mark in the 4th box will put roflblack instead of a little guy laying on his back and side laughing.