The ornamental design for a radiatorgrille for an automobile, as shown and described.
FIG. 1 is a front elevational view of a radiator grille 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 broken line showing of the radiator grille is for purpose of illustrating environmental structure and forms no part of the claimed design. The rear view of the radiator grille forms no part of the claimed design.