.directive('flag', function($compile) {
    return {
            restrict: 'E', // this means it will be an element
            scope: {
                current: '=current'
            },
            template: '<span class="flag-icon flag-icon-{{current}}"></span>',
            link: function(scope, element, attrs, ctrl) {
            }
        };

// se usa:
<flag current="'EEUU'"/>