The ornamental design for an exterior facing surfaceconfiguration of a trunk for an automobile, as shown and described.
FIG. 1 is a front view of an exterior facing surface configuration of a
trunk for an automobile according to my novel design;
FIG. 2 is a top view of an exterior facing surface configuration of a trunk
for an automobile according to my novel design;
FIG. 3 is a side view from the left of an exterior facing surface
configuration of a trunk for an automobile according to my novel design,
which is a mirror image of the side view from the right; and,
FIG. 4 is a perspective view from the front right of an exterior facing
surface configuration of a trunk for an automobile according to my novel
design.
The broken line showing depicts environment and is not part of the claimed
design.