If you are going to make blocks to be signed, then you definitely want to back them with freezer paper. You also want to put 1/4 tape on the front around the edges so that signatures do not get written in the seam allowances. Obviously this means that the quilt will not be completed at the wedding.
I did a signature/photo quilt for my parents 50th wedding anniversary as a surprise. I started about 2 years before the anniversary. I picked a pattern and cut the light squares. Backed each one with freezer paper and taped the edges. I then shipped a bunch of them to family/friends out of state with the Pigma permanent fabric pens and instructions to use those pens only. I also gave a bunch to a friend at their church and asked them to be signed. I caught some people at my dad's 70th birthday party.
In the meantime, I gathered photos from their lives and printed them on fabric. When I got the signature squares back I constructed the quilt top and quilted it. I did discover that at least one person did not use the pens I provided. I discovered this when I sprayed the square with starch and the ink ran - ouch! Luckily I was able to fix the problem. The quilt ended up as a queen size quilt.
I did a presentation of the quilt at the anniversary party.