Some social media users claimed that it was a viral marketing stunt while others suspected vandals or even a tech-savvy artist making a statement.

Cemeteries in Munich allow QR codes as memorials on headstones, Mr. Hoerauf said, and for more than a decade, people whose loved ones are buried in cemeteries around the world have uploaded photographs and other digital keepsakes to create online memorials that can be viewed via QR code.

More than 1,000 stickers were put on gravestones and wooden crosses at three cemeteries in the German city, without any indication of where they came from or why. The 5×3.5-centimeter (1.95×1.2-inch) stickers are printed with a QR code,

More than 1,000 stickers have appeared on gravestones at three cemeteries in Munich, Germany, without any indication of where they came from or why, sparking a police investigation