BERLIN—German flags have sprouted like red, black and gold wildflowers across Berlin this summer. They're appearing on balconies, cars, bicycles, storefront windows, even painted on children's cheeks. Few can match Youssef Bassal's.

Eager to show his enthusiasm for Germany's soccer team during the World Cup, Mr. Bassal, a 38-year old Lebanese immigrant, unfurled a 60-by-15-foot German flag a few weeks ago, on the facade of the building that houses his cell-phone store.

Mr....