The SPD in the logo is in reference to the German, not French, social democratic party (Sozialdemokratische Partei Deutschlands).

With the subscript and arrows the SPD logo is turned into NSDAP, which was the Nazi party.

“Wer hat uns verraten? Sozialdemokraten!” (Who betrayed us? Social democrats!) is a German rhyme in reference to their behaviour during the Third Reich specifically, but also their general tendency “umzufallen” (to tip over) when they are in a coalition and should stand their ground on social issues.