hehehehe that are rank images.
They are corresponding with the rank below your avatar.
These are the ranks:

0 - 10 posts: New Castaway (1 bar)
10 - 20 posts: Castaway (2 bars)
20 - 100 posts: Found the Hatch (3 bars)
100-200 posts: Hiding for the Others (4 bars)
200-400 posts: Found the Black Rock (5 bars)
400-750 posts: Blew up the Hatch (6 bars)
750-1500 posts: Building a raft.. (7 bars)
1500+ posts: Survivor (8 bars)

And theres also moving bars for moderators and admins.

__________________
Webmaster LOSTTalk.net