More than 1,000 stickers were put on gravestones and wooden crosses at three cemeteries in the southern German city of Munich.
The stickers, which have been put on both old and recent graves, have a QR code that when scanned shows the name of the person buried and the location of their grave in the cemetery.
The 5x3.5-centimeter (1.95x1.2-inch) stickers surfaced in recent days at the Waldfriedhof, Sendlinger Friedhof and Friedhof Solln cemeteries.
Police are investigating the incident.
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"We haven't found any pattern behind this yet. The stickers were put both on decades-old gravestones and very new graves that so far only have a wooden cross," police spokesperson Christian Drexler said.
"People who have witnessed anybody putting the stickers on the graves are asked to reach out to the respective cemetery's administration," Mr Drexler said.