The ornamental design for a window-mountable flag and light, as shown and described.
FIG. 1 is a front elevational view of a window-mountable flag and light showing my new design, the rear elevational view being a mirror image thereof;
FIG. 2 is a bottom plan view thereof; and,
FIG. 3 is an illustration of my design in use.
The showing of words "HELP" and "TOW" in FIGS. 1 and 6, of batteries in FIGS. 3 and 4, and of a vehicle in FIG. 5 is for illustrative purposes only and forms no part of the claimed design.