I have done a couple signature quilts. One for a retirement and one for our son & daughter-in-law's wedding.
I ironed freezer paper on to the back of my fabric and then cut fabric into the size I needed.
Then I made picture frames out of cardboard that allowed for the seam allowance. People slipped the fabric underneath and signed in the box. It worked quite well and most people managed to stay inside the seam allowance.
I also used the pigma ink pens. Some are better then others the jel ink ones seem to be the best. Scrapbooking stores carry alot of this type pen.
Good luck and make sure you post pitures.