def METHOD_NAME(self, topo_id):
    sig_cfg = {"ConfigVersion": 1, "ASes": {}}
    for t_id, topo in self.args.topo_dicts.items():
        if topo_id == t_id:
            continue
        sig_cfg['ASes'][str(t_id)] = {"Nets": []}
        net = self.args.networks['sig%s' % t_id.file_fmt()][0]
        sig_cfg['ASes'][str(t_id)]['Nets'].append(net['net'])
    cfg = os.path.join(topo_id.base_dir(self.args.output_dir), "sig.json")
    contents_json = json.dumps(sig_cfg, default=json_default, indent=2)
    write_file(cfg, contents_json + '\n')