Please check your wallet with the "getblockhash" commands we posted earlier to see if you are on a fork. As already said, this symbol means that you found a block on your own, which is theoretically possible, but with 1% CPU highly unlikely.

Btw: the main pool also seems to be on the wrong chain, it constantly changes the given information like "coins mined", "offline workers" etc. and also seems to be quite unresponsive.