Flag the individual inventory items in the system. 

Individual inventory items must be flagged or identified as serialized inventory items.  There are two fields in the Inventory Master File which are used to indicate whether each item is serialized and to indicate whether the item is to be serialized upon receipt or only when it is sold.  The Serial field in the Inventory Master File (file 70) indicates whether the item is a serialized inventory item.  A "Y" should be entered into this field for all serialized inventory items.  A blank or an "N" in this field indicates that the item is not a serialized inventory item.  The Serial_Receipt field in the Inventory Master File (file 70) indicates whether the inventory item should be serialized as received into inventory or only as the item is invoiced to a customer.  If a "Y" or a blank is entered into the Serial_Receipt field, the system will prompt the operator to input the serial number of the item when it is received into inventory, if a "N" is entered into the field, the system will not prompt the operator for serial number input as the item is received (it will only prompt the operator for serial number input when the item is invoiced). 

More:

Serialized Inventory System Startup Checklist