Before you get to sending your cards away to get signed, you want to ensure that you have prepared them properly. For cards without a glossy finish, you can be fairly certain that the ink on the card will be a nice, solid color when using a sharpie. For the cards which have a glossy finish, you have one of two options that I’ve tried.
Option 1: Use an eraser – Take any white standard eraser and practice on a card that you don’t mind if it gets ruined. Once you know that the eraser doesn’t damage the practice card, on a regular card, rub the entire surface of the card in case the player decides to sign on some corner of the card.
Option 2: Use baby powder – I prefer using baby power but it does leave my tables full of white powder (yikes!) after I prep my cards. I usually splash a dash of baby powder on my card and rub with a tissue. Of course, you’ll also want to test on a card you don’t mind ruining so you know how much powder to put on and how hard to rub.
Obviously, either option 1 or 2 is a personal decision. Experiment with both before you use either option on any cards that you want to get signed. To know if you’ve done a good job in removing the gloss, you can rub your finger across the card and if it feels like it has a bit of resistance to the movement of your finger, then you should be okay to send it through. After a bit of practice, you’ll get the hang of it.