From the FAQ:
The balloons under your username indicate your "rank" on Clown Forum. You earn more balloons by making more posts.
The images under usernames are awards for various forms of participation in Clown Forum. For instance, you can earn the heart badge by linking to Clown Forum from your web page, or the video award by posting video tutorials. Some awards are only given out after a contest. See the Awards List (
Clown Forum - Awards) for a full list of the awards you can win.