FORD 2003 Expedition v.1 - Manual (Page 189)

Your vehicle has LATCH anchors for child seat installation at the seating
positions marked with the child seat symbol:
Never attach two LATCH child safety seats to the same anchor.
In a crash, one anchor may not be strong enough to hold two
child safety seat attachments and may break, causing serious injury or
death.
The lower anchors for child seat
installation are located at the rear
section of the second row seat
between the cushion and seat back.
The LATCH anchors are below the
locator symbols on the seat back.
Seating and Safety Restraints
189