Eduard often produces their own decal sheets for their kits.  Occasionally, they also offer stand-alone sheets.  This small decal set contains four WWII-era national insignias for the P-51D Mustang.  Two of these go on the fuselage and the other, marginally larger pairs of stars and bars are destined for the wings.

These decals can be used on any P-51, of course, and this style of national insignia was used between August 1943 and January 1947.  So, if you need more Mustang national insignias for any reason, you’ve got a solid resource here.  Perhaps you goofed up the ones in the kit or maybe a P-51D kit (such as with Eduard’s Overtree boxings) where you’ll need markings.  In any event, this set has you covered.  Furthermore, decal quality looks great, from colors to print quality, register, and restrained carrier film.