Rick and Morty did this once, Rick simply put on a hat with a QR code that made a robot army recognize him as a high level commander.

A few days ago I read a short story, comp.basilisk.faq by David Langford, which sketched a world in which specific images could irreversibly crash the brain, leading to a full scale worldwide ban on images on the internet and many other places as well. The story postulated hundreds of potential info-hazards with many of them simple enough to be applied via stencil and spray paint. Two of them are branch families of the Mandelbrot set ‘and no we won’t tell you where, do not look’

Other examples; Snow Crash — Neal Stephenson Blit — David Langford The Atrocity Archives — Charles Stross Doctor Who — “Blink” / “The Time of the Doctor” SCP Foundation — SCP-096 SCP-7387 (“The Mathematician’s Grin”)

“Keep your eyes peeled or we’ll peel them for your wholesale!”