"Thanks for buying my book. It's people like you who make this all worthwhile! Together we can achieve our dream of a chicken in every yard. Then after that, we can achieve our secondary dream of a rooster in every stew pot." Then you can hand-draw a chicken, color it in with the colors of their choice, and sign your name in a word bubble that is coming out of the chicken's mouth.
If there are a lot of people in line, you can write "zzolollzz" which is what it will look like anyways after the tenth one.