These message cards look a bit like QR codes until you raise them to eye level and read the “magic message” from bottom to top. The bottom is indicated by a number. Start at part 1 of the two-part message.
Decades ago, these things took me forever and a day to draw by hand. But then I could legitimately challenge my students to draw a message of their own. Nowadays I use the computer so they take less than an hour to make. Unfortunately, that means that I’ve lost the moral authority to issue the drawing challenge. But the “wow” moment when a student actually sees the message still makes it worthwhile.