please don't use a sharpie. i am afraid they contain acid and that will eat into your fabric in future yrs. may take a generation, but we are quilting for our future family.
only archival quality markers should be used on our precious quilts. better to use nothing than use something that will damage in the future.
we all work too hard to take a chance.
unless the company that makes sharpies can promise that they are acid free, we should stay far away from them.