Well let's see.
The king would be some kind of tiny club. Simply invert it, and whack away with the weighted base. So much the better if you're triple weighted for tournament play.
The queen would be some other kind of tiny club. Excpet with no jaggy bit to dig into your palm.
The rook? A nice, thick, tiny club. A bit short, but maybe good for people with tiny fingers and stout hands. Like if you hang out with Tolkienian dwarves. Or midgets.
The bishop, being nice and pointy on top, is probably better used for stabbing into people's eyes.
The pawn would be another kind of tiny club.
Knights are useless, but could probably do in a pinch as some sort of crude projectile. Throw it, see what happens.
If chess pieces were weapons, what would they be?