"the police wouldn't have known it" - in which case they were quite remarkably ill-informed, given all the preparation for the World Cup. And it's not exactly hard to find out even if they didn't know in the first place - just type "Harki" into Google, and see what comes up. Takes all of two seconds. The German police force does surely have computers.

"Quisling" would be a racist term for a player of Norwegian extraction playing for Germany. Similarly with "Kapo" for a Jewish player doing the same. When used by people of the same ethnic group these could indeed be political insults rather the racist - but in this case of these Italian banners the message implied would clearly have been "Zidane isn't even French, he's an Algerian - and he's a devalued sort of Algerian at that."