In 2003, David Foster Wallace sent in his subscription card for the then-new arts and culture magazine The Believer. Ever the English professor, Wallace included plenty of corrections and notes. The card comes from a McSweeney's collection recently obtained by the Harry Ransom Center at the University of Texas, and you can check it out below:

The University of Texas

His notes:

In the box for "Check Enclosed": "How, with a postcard?"
In the space for his credit card number: "Are you kidding? On an open postcard?"
He goes ahead and makes his own box, which he checks off: "Bill Me!"

Knowing Wallace's proclivity for writing postcards, this was clearly a medium he was comfortable in.