Samurai: suits of armor, and different sword racks on the walls.
Dustari: giant stone knight-looking statue things.
Forest: umm...not too sure about this...maybe potted plants?
Zormite: Giant Merman looking statues, or giant ice-tridents, like mentioned before.
Crescent Pirates: Maybe the giant cross-bone sails on the walls, and those other things mentioned before, maybe some pictures on the walls of successful naval battles of the CP.