The good news with regard to removing permanent marker from a metal surface is that it is easier to remove Sharpie from nonporous surfaces. This is a guide about removing permanent ink (Sharpie) from metal.
How do you remove red Sharpie from a brass doorknob?
By joshnoodle from Mauldin, SC
Alcohol or denatured alcohol should do it.
I haven't tried it myself, but read recently that if you go over permanent marker with dry erase marker, then rub it off with the dry erase brush both marks will be removed. Good luck.
In a hidden place take the sharpie and make a mark, let it dry then write over the mark again and quickly wipe both marks. The new ink should remove the old. You may have to do this more than once. If it satisfies you here, go to the real mark you need to remove and repeat without letting the ink dry. Also try nail polish remover, again in a hidden place always when experimenting.
Oh my god thank you so much! This worked so well and got it off so quickly!!!
How should I go about removing Sharpie from an old tin lunch box without removing the paint?
Just a suggestion try clean the marks off from the inside. Tin should be thin enough for the derutent hot water wax. Which they use for cleaning spray paint off walls. Thanks for your hits and tips.