So called "permanent" markers are water insoluble. They are easily removed with most any kind of non-water based solvent such as paint thinner.
Use a slightly damp paper towel to remove a bit at a time. This will probably remove some of the finish on the case as will most of these solvents.
Here are some other things you can use:
- Liquor such as bourbon (101 proof)
- Toothpaste (Sprinkle a bit of Baking Soda on it. Mix together.)
- "Magic Eraser™" (That's the product name.)
- Dry-Erase marker (It has a solvent in it.)
- Pencil eraser (There are different types. Avoid abrasive "ink" types.)
- Sunscreen cream
- Nail polish remover
These will not scratch the surface of the metal case if you don't rub too hard.