How much time do you have? I made an autograph quilt for in-laws 50th wedding anniversary. I had everyone sign in pencil and embroidererd over the pencil w/ floss, to match the colors of the various blocks. I did not worry about washing/laundering as it hangs in their hallway.
Just a few hints: Ask for them back earlier than you need them--you always have your stragglers and mine were from one of their KIDS!! Provide specific instructions on how, where and WHAT to sign. you wouldn't believe the phone calls on "What should I write?" When in doubt, just sign your name. I also provided a few samples on the paper so people could see exactly what I wanted.
HTH and good luck. I'm sure it'll be treasured for years to come.