Black Sharpie on Civil War Sword?
So, I have a very nice Schuyler Hartley NY sword in otherwise decent condition that appears to be Civil War era, no scabbard, some pitting on the end of the blade but otherwise the metal has aged appropriately and hasn't been cleaned or restored. It was taken as evidence for a while (not my fault) and eventually returned with the evidence numbers written in black Sharpie down the blade. As far as I can tell, the marker has been on there for just about 12 months.
Should I take it off, and, if so, how would I do that without damaging the blade or the patina?
Acetone or ordinary lacquer thinner on a paper towel should wipe the marker off without harming the patina.
Rub gently to dissolve the marker.
Markers can't "soak into" the metal and lacquer thinner and Acetone can't harm metal.
At worst, any grease on the blade will be removed.
After cleaning off the marker, do what museums do to protect old weapons and armor..... apply a coat of Renaissance Hard Carnuba wax.
This was developed by museums specifically for this purpose.
Buy it from Brownell's, some wood working supply houses or online.
You can also use Johnson's Paste Wax, available at most any hardware store or Walmart.
Would the blood of the bureaucrat who marked it take it off?
No, you must leave it on there... anything on the blade for 1 year or more is officially and permanently part of the patina and may never be removed without the risk of irreversibly damaging the value as appraised by "The Antique Road Show"... SOOOOO, what ever you do, keep that sword blade far away from any hydrocarbon solvents like mineral spirits, lacquer thinner, etc... [/sarcasm]

Even denatured alcohol will remove it.
Rubbing alcohol would work and would be less harmful than acetone or lacquer thinner.
Use a regular ol pencil eraser , it will come right off.
lol, please don't actually use an eraser. poor patina.
Seriously though, anything from a little vodka to acetone (nail polish remover if you don't have straight acetone around but there's a gal in the house) will do the job. Use a soft clean cloth or a paper towel, but be GENTLE. You can mar the blade and leave a visible mark if you aren't gentle. Let the solvent do the work more than any friction from the cloth.
Don't delay afterward when it comes to a protective coating. The Ren-wax suggestion is a great one. I use Min-Wax furniture paste wax, but almost any basic canuba based wax will do the job, you just don't want one with a bunch of additives like some of the car waxes. Apply as per the instructions, usually they're for wood but it works the same. In most cases it's "wipe on, making sure to get it everywhere you want to protect. wait a bit for it to dry. gently wipe/buff to a pretty finish." The key is to not take it off completely in that last step.
Thanks!
How about a picture ?