The circle represents your Overall rating. This includes all rated games.
The lightning bolt represents your Blitz rating. This includes only those rated games with Blitz time standards (faster than 12 seconds per move).
The clock represents your Live rating. This includes only those rated games with Live time standards (starting at 12 seconds per move and under about 4 hours per move).
The turtle represents your Correspondence rating, This includes those rated games with Correspondence time standards (over about 4 hours per move).