If that's caused by the brass being ejected, try cleaning your pistol more often. Brass can indeed mark hardened steel if there's dirt or carbon build up in the area. Brass tubing is often used to drill holes in glass. All it takes is a little abrasive.

Billboard? Can't be any worse than the paint-on filigree done to some pistols.

Addition:
Don't load dirty ammo.
Don't drop your magazines in the dirt