The art of hiding clues in seemingly normal poetry. Typically, there are a few key words (such as the first word on every line or every word that is capitalized) that string together to make another sentence with hidden meaning.
Someone, a Jon Doe,
Is wearing glasses,
Reading and studying cryptopoetry. Poring
Over the poem, he tries to find
Your clue, but it is too difficult. His
Shoulder slumps down in failure.