GMC 2008 Sierra 1500 Pickup Owner's Manual page 62

Driver Side shown, Passenger Side similar
The roof-rail airbags for the driver, right front passenger,
and second row outboard passengers are in the
ceiling above the side windows.
1-58
CAUTION:
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If something is between an occupant and an
airbag, the airbag might not inflate properly or
it might force the object into that person
causing severe injury or even death. The path
of an inflating airbag must be kept clear. Do
not put anything between an occupant and an
airbag, and do not attach or put anything on
the steering wheel hub or on or near any other
airbag covering.
If your vehicle has roof-rail airbags, never
secure anything to the roof of your vehicle by
routing the rope or tie down through any door
or window opening. If you do, the path of an
inflating roof-rail airbag will be blocked.