I would steer away from sharpie markers even though they might say permanent. I would stick with the Pigma Micron pens. I was trying to make a label for DGD's quilt using the Sharpie markers and was not pleased, as they bled onto the muslin fabric I was intending to use. On the other hand, I have quilts with labels that were made in the early 1900's that are still legible after repeated washings. That's been my experience at least. One word of advice, regardless of which pen you decide on, I would iron a piece of freezer paper, slightly smaller than the charm square which would help the writing on the charm square.