Under US law, certain companies are required to file with the US Securities & Exchange Commission (SEC) a report that describes their efforts to responsibly source tin, tantalum, tungsten and gold (3TG) from the Democratic Republic of the Congo (DRC) and surrounding countries - called a "Conflict Minerals Report". If a company's Conflict Minerals Report also covers other minerals this would be a good sign that they take the issue seriously and are willing to go beyond the legal requirements.
This metric is asking whether the company's Conflict Minerals Report covers diamonds.
Search the company's Conflict Minerals Report for the word "diamonds". If diamonds are mentioned, read the surrounding information to determine if diamonds are simply mentioned in passing (e.g. in the name of one of their smelters/refiners) or whether the company is taking steps to source copper responsibly.