"SS units "Deadhead" (SS-Totenkopfverbände or SS-TV) — special SS units that guarded concentration camps. The image of the "death's head" (skull and crossbones) was worn not only as a cockade on the cap, but also in buttonholes. The units were stationed in camps in Nazi Germany, such as Dachau and Buchenwald, in Auschwitz in Nazi-occupied Poland and in Mauthausen in Austria, as well as in many other concentration camps and death camps."
In short, it was the SS sub-divisions in Nazi Germany that were mainly engaged in racial cleansing on the territory of conquered Europe and parts of the USSR.