Many pens in the market are good, but I doubt you will find anything that will stand to repetitive laundry, especially with the detergents that we have now a days. When I thing of a signature quilt I prefer to think of a wallhanging or a large quilt that will be hung on a wall or even framed and out of direct sunlight. Even the best marker will fade when exposed to water and detergent often. I saw someone use the signatures as a pattern and embroider over each one to preserve it.
Maybe someone else will proof me wrong.
Maria