What do the so-called "Stolpersteine" (stumbling stones) in Germany commemorate?

1. famous German politicians
2. the victims of National Socialism ✓
3. traffic fatalities
4. well-known Jewish musicians

These small brass plaques are placed in the sidewalk to honor the memory of people persecuted by the Nazis. It is a touching way to keep their names alive in the neighborhoods where they once lived!