HALLE, Germany — Christmas carols were playing and the scent of ginger hung in the crisp December air. Students sold organic plum compote and served mulled wine in biodegradable cups made from sugar cane. But then there were the postcards.

“Islamization? Not with us,” read one. “Defend yourself! This is your country,” urged another. “Fortress Europe,” said a third. “Shut the borders.”

This was no ordinary Christmas market, but one hosted by Generation Identity, a far-right youth movement under observation by several European intelligence services. Part hippie, part hipster, the activists of Generation Identity are one result of a broad image makeover the far right has tried to give itself in recent years.