I have used a pencil eraser on some brass marks with good results.
But, IMO, a pristine SD firearm is a sign that could be read that the owner does not carry or practice much. I want a BG to see a well used weapon so he believes that I may know what I doing.
Keep the mark and add more.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Life Member NRA
Life Member NAHC
Former President of the ECPT (Eifel Combat Pistol Team)