The best advice is to TEST FIRST on a scrap piece of fabric of the same fabric. If you've pre-washed the project, then pre-wash the scrap before testing.
We had one member of our guild have everyone bring in their marking pens. At the top edge of the fabric sample she wrote down the name of the pen, then drew a long line down the fabric. After gathering different pen marking samples she then washed the fabric sample. The fabric sample was about the size of a placemat made out of either kona cotton or muslin.
She had the sample edges turned over with a narrow hem sewn.
It was very interesting to see the outcome of the different marking pens.
This might be a good project for a guilt guild/club to work on as a group with one member making up the placement before beginning. The outcome in a picture could then be posted on their webpage and/or shared with the members so they would have the outcome as reference.
There are also some very good marking pencils now where the lead markings disappear with just plain water.
Good Luck with your project.
Pam M