The stone from the Klooga concentration camp.

The date says 6.9.1944.
When the Soviet army began its advance through Nazi-occupied Estonia in July and August 1944, the SS started to evacuate the camp. Many prisoners were sent west by sea to the Stutthof concentration camp. Around 2000 prisoners were killed, their bodies were stacked onto wooden pyres and burned. The camp was liberated by the Soviet army on 28.9.1944, only 22 days after the writing on the stone.
The stone is in the Estonian Jewish museum