The company that designs them is called Three Squares Greetings (you can order the cards from their website), and they trade on a niche that’s clearly been overlooked by the Hallmarks of the world. “Wish you weren’t there!”
Mental Floss asks:
Anyone else ever had a little writer’s block while penning a note to a loved one in prison? (Feel free to comment anonymously, if you feel like it.)
And from the Los Angeles Times:
"I know that I have not visited you. But I still care about you. . . . When are you getting out anyway??"