As a figure of speech, a common meaning of the term "unmarked grave" is consignment to oblivion, i.e., an ignominious end. A Grave (burial) monument (or headstone) is a sign of respect and fondness, erected with the intention of commemorating and remembering a person. Even when a person's remains are lost, a cenotaph may be erected. Conversely, a deliberately unmarked grave signifies disdain and contempt. The underlying intention of an unmarked grave is that the person buried in it is not worthy of commemoration, and should therefore be completely ignored and forgotten, e.g., Heinrich Himmler.
Unmarked graves have long been used to bury executed criminals. More recently, the practice has been to cremate and secretly scatter the ashes of notorious criminals in some anonymous place. This was the fate of Nazi war criminals such as Herman Goering, Fritz Sauckel, Julius Streicher and Adolf Eichmann. The remains of British serial killers Myra Hindley and Dr Harold Shipman were also treated in the same way. Cremation and secret scattering of the ashes has the additional effect of removing all possibility of there being a grave for someone to visit in the future.