In previous of versions of Dynamics AX like 2009, there was field called Direction on the InventTrans table which determine the direction of the inventory transaction. It can have either the following possible values: Issue, Receipt or None.
In AX2012 the Direction field has been removed from the InventTrans table. Instead, a new display method direction has been added to the InventTrans table. This display method returns the same values as previously the Direction field was.