I just did this for my mom's 80th. I used the pigma pens but the larger 05 size, not the 03. I drew in pencil the seam lines and people still went outside the lines! LOL I ironed freezer paper to the back for stability. You do have to heat set the ink with a hot iron.
I used a simple 6" block. If you just want signatures, specify that. We have lots of wonderful sentiments on hers, but then they signed, 'love Joe', etc. Right now we know who they all are, but I made a chart for her with exactly who signed where. The drawings were great too. Mom loves it.