The ornamental design for a rearbumper for an automobile, as shown and described.
FIG. 1 is a front elevational view of a rear bumper for an automobile showing our new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a front and left side perspective view thereof; and,
FIG. 7 is a front and right side perspective view thereof.
The rear view of the rear bumper forms no part of the claimed design. The inside surfaces of the rear bumper, shown in broken lines in FIGS. 2, 3, 6 and 7, form no part of the claimed design since the inside surfaces are hidden when the rear bumper is mounted to the automobile.