The ornamental design for the rack mounted warning light, as shown and described.
FIG. 1 is a perspective view of a rack mounted warning light showing our new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 front view thereof;
FIG. 5 is a rear view thereof; and,
FIG. 6 is a right side view, the opposite left side view being a mirror image thereof.
In FIG. 5, the entire region containing broken lines and the elements in broken lines in all other figures depict environmental subject matter and form no part of the claim.