I also make my labels mostly out of muslin, sometimes framed in scraps of the fabric used on the top. I use permanent fabric markers. It helps to iron the muslin onto a piece of freezer paper. It stabilizes the fabric so it doesn't wiggle around as you write. I usually write out what I want to include on a piece of paper first so I can get the wording and spacing just right before I put it in permanent ink on the fabric. Of course if you mess it up, you can always get another piece of muslin. I usually include the date I completed the quilt (not the date started, lol) who it is for, the occasion, and sometimes include the city and state. You might even include a dedication of some sort, a Scripture verse or a quote that fits the occasion. You have created an heirloom, imagine what sort of information would be interesting to people years from now who might wonder about the quilt's history and you, it's maker. When I see old quilts at estate sales or antique stores, I always wonder who made and if there was a special occasion for it. Why did they choose the colors or pattern, etc. etc.