if ($http_referer ~* spamdomain1.com) {
    return 444;
}
if ($http_referer ~* spamdomain2.com) {
    return 444;
}
if ($http_referer ~* spamdomain3.com) {
    return 444;
}

map $http_referer $bad_referer {
    default                  0;
    spamdomain1.com          1;
    spamdomain2.com          1;
    spamdomain3.com          1;
}

if ($bad_referer) {
    return 444;
}

if ($http_referer ~ "spamdomain1.com|spamdomain2.com|spamdomain3.com")  {
  return 444;
  break;
}