antifainternational:

Via Brighton Antifascists: 

KNOW YOUR ENEMY – Some of the symbols, codes and numerals used by the far-right. If you spot any of these being used as tattoos, on social media etc, it’s a fair bet you’ve got yourself a fascist.

More info here: http://bit.ly/2fRVIuE and here: http://bit.ly/2fWu7qd 

As always though, use should ALWAYS be taken in context. For example the Valknot symbol that looks like three intersecting triangles is also used by people who practice Asatru or Odinism, because nazis love using ancient European imagery.