WARNING: This page is about a different car, the 2008 Subaru Impreza. However, it is still accessible from the selected car via links, so may be relevant.
Wagon model
Fig 1: Identifying Curtain Airbag Module - Wagon Model
Courtesy of SUBARU OF AMERICA, INC.
Sedan model
Fig 2: Identifying Curtain Airbag Module - Sedan Model