code: public static base_responses sign(nitro_service client, dnszone resources[]) throws Exception {
  		base_responses result = null;
  		if (resources != null && resources.length > 0) {
  			dnszone signresources[] = new dnszone[resources.length];
  			for (int i=0;i<resources.length;i++){
  				signresources[i] = new dnszone();
  				signresources[i].zonename = resources[i].zonename;
  				signresources[i].keyname = resources[i].keyname;
  			}
  			result = perform_operation_bulk_request(client, signresources,"sign");
  		}
  		return result;
  	}
docs: Use this API to sign dnszone resources.