The full signature is:

    My Custom Sets
    
    Avant Block: Avant -- Stormfront

Which suggests that it's the name of the in-progress second set of a block of custom user-created cards the person is working on. Quick glance at the posts the signature links to gives me the impression it was chosen simply as a generic "storm is coming" fantasy-setting name.

And for people who know a bit about Magic: seems a lot like "Scars block without the Phyrexians", even down to the user posting a variation on Koth.

It doesn't appear to be anything obviously associated with the Nazi group, though.