You can try using rubbing compound (automotive) applied with a rag and rubbed vigorously. I would not try anything more than that as it might give the appearance that you are trying to remove the serial number.
Your other choices are "0000" steel wool, polishing compound (automotive), or toothpaste.
Toothpaste is the least abrasive and probably won't do much.
Ditto for polishing compound.
The steel wool in 0000 may make the surface look over-shiny.
A light application of "wet or dry" 600 or 1200 grit will be more aggressive. Use with water or oil. Use the one that matches the finish on your gun most accurately. The 600 will look more like satin; the 1200 will look more like a mirror.
I would not use a Dremel tool or other tool as it will take off too much material.