From the NannyMUD documentation

LAST CHANGE

2001-01-06

FUNCTION

NAME
        is_weapon - is the object a weapon?


LOCATION
	/std/simple_weapon, /obj/weapon

SYNTAX
	int is_weapon();

DESCRIPTION
	This function returns 1, and thus mark the object as a weapon. It
	should be defined by objects that are true weapons, i.e. that will
	handle all things a weapon should. This means basically weapon objects
	in the lib.


RETURN VALUES
	1 - marks the object as a weapon