public String toString(String pad) {
    StringBuffer sb = new StringBuffer();
    for (Entry<String, Object> e : sigMap.entrySet()) {
      sb.append(pad);
      sb.append(e.getKey());
      sb.append(" = ");
      sb.append(e.getValue());
      sb.append('\n');
    }
    return sb.toString();
  }
Holds the signature of the operator; the keys are are the methods name marked by {@link Signature}.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/signature/OpSignature.java