If the fact that it is C.C.'s blood on the piece is significant, it means that by the time Lelouch wins, C.C. will have died for him or as a result of his actions.
If the fact that it is C.C.'s blood is not significant, it is merely symbolism that suggests that Lelouch will be drenched in blood before this conflict is over.
This scene also tells us that Lelouch will win, since the Black King stands while the White King does not. However, since most of the pieces on both sides are knocked over, it suggests that just about everyone will die on both sides.