Provides that for the purposes of weapons prohibited in certain courthouse areas, "weapon" means any firearm, explosive as defined in RCW 70.74.010, or any instrument or weapon of the kind usually known as slung shot, sand club, or metal knuckles, or any knife, dagger, dirk, or other similar instrument or weapon that is capable of causing death or bodily injury and is commonly used with the intent to cause death or bodily injury.