The ornamental design for a lightbar for a motor vehicle, as shown and described.
FIG. 1 is a front elevational view of the light bar for a motor vehicle, with the center portions broken away to indicate indeterminate length;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a right elevational view thereof;
FIG. 4 is a left elevational view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is an enlarged view of the area 7 in FIG. 1;
FIG. 8 is an enlarged view of the area 8 in FIG. 1;
FIG. 9 is an enlarged view of the area 9 in FIG. 1;
FIG. 10 is an enlarged view of the area 10 in FIG. 2;
FIG. 11 is an enlarged view of the area 11 in FIG. 2;
FIG. 12 is an enlarged view of the area 12 in FIG. 5;
FIG. 13 is a cross-sectional view along line 13 in FIG. 7;
FIG. 14 is a cross-sectional view along line 14 in FIG. 9; and,
FIG. 15 is a cross-sectional view along line 15 in FIG. 7.
The broken lines depict environmental subject matter only and form no part of the claimed design. The dot-dot-dash chain lines indicate enlargement areas and form no part of the claimed design. The appearance of the portion of the article between the bracketed break forms no part of the claimed design.