Someone had done this years ago at work. They were houses with a rectangle for everyone to sign. It was already made into a quilt. With using batiks, I would make the signature square cotton while the rest is batik. Perhaps someone here knows whether you can write on batiks or not. If the signature square (or rectangle) is small enough (say 1 1/2 by 2 1/2) you can quilt around those blocks not in them and should be safe for recommendations on most batting .
Then the day of event someone might want to watch and make sure people are signing in the squares or rectangles.