I'm in the middle of editing the first book of my Draper & Blackwell mystery series. In the book, the readers can do one of two things.
1) Solve a series of codes (which will be placed at the beginning of the book)
2) Read for pleasure
Whether you solve the codes or not, the answer will be given at the end.
Anyways, if some want a crack at solving the codes, here they are (click on them to enlarge):
Also in the book there is something called the Yuri Code. You can try and crack it too. The link is here.