I think the ~ means that you havn't played I certain amount of games I think under 10 or 15 or 20 I don't know but I think it means that. The 0 is your actual ranking so I figure that your score is ~0 when you log in because you havn't played a certain amount of games yet and you are losing more than you are winning. But i'm still learning.

How often do you play? FlyOrDie sometimes reduces your score if you go long times without playing.