Not super on-topic, but this reminded me of a thing that Games Magazine used to do called the "Hidden Contest". Great fun.

https://en.wikipedia.org/wiki/Games_World_of_Puzzles#Contest...

> In the past, the magazine also ran an occasional hidden contest, in which part of the challenge was to find the concealed puzzle with instructions on how to enter (e.g. "You have found the hidden contest. To enter, send us a chain of paper clips."). Until November 2002, readers were also challenged to find the fake advertisement among the legitimate ones (the last one was for the Red Card, a credit card used to pay off credit cards).