ISO/IEC 15939 favours the concept of an indicator. An indicator can come in many flavours and colours, but its main purpose is to serve as a metrics with interpretation.
Six Sigma has two related concepts: the concept of metrics in DMAIC and the concept of controlling. Using run-charts or Pareto-charts requires further interpretation and this is where the indicators come into play. The indicators can help the users of Six Sigma to judge whether the information require action or not.
So, ISO/IEC 15939 and its concepts of indicators can be a great deal of help to the users of Six Sigma - taking down the costs is just one of the applications.