I use Pigma Pens. They are not supposed to fade when you wash the quilt, but I think they do a little. I like to use a good quality muslin, heavily starched, and unfortunately, expect some people to write over the seam line, even if you mark it with pencil or stitching. Just can't be helped because if they don't quilt or sew people don't think about why they can't write all the way across. Also I would mark the seam line about 1/2" if possible.