From the NannyMUD documentation

LAST CHANGE

2001-01-06

FUNCTION

NAME
        is_money - the object defining this is a money object


LOCATION
	/obj/money

SYNTAX
	int is_money();

DESCRIPTION
	This function returns 1, and thus mark the object as a money. There is
	really only one object, the libs money object, that should define this
	function. There are severe problems with money handling, if you are
	not absolutely sure of what you are doing, don't. If you are sure, be
	safe and discuss your object with the admin first.


RETURN VALUES
	1 - marks the object as money