What's this symbol used by the Nazis?
This is the symbol of the Sturmabteilung,  a paramilitary organization within the German Nazi Party, whose methods of violent intimidation played a key role in Adolf Hitler's rise to power.

It's made up of an "S" (in lightning bolt shape) and an "A" and is probably a reference to Neo-Nazi groups evading the Swastika ban by using other related symbols.