I would recommend
Brillianize and some of
these lens wipes. Don't use Windex, it will leave a residue on the flags. Don't use paper towels, they will leave all sorts of schmutz on the flags. If there's a lot of oil on them, isopropyl alcohol (70% or higher) first, but keep it away from the glue holding the flags to the metal. If you have any tough areas to reach, try
these.