Template:+source
The Template:+source is an informational template that marks articles that cover a topic from official or semi-official sources but are still without source references (source index or citation). All marked articles can be found in Category:!Missing Sources.
What to do?
If someone knows the sources on the topic, they can add them and then remove +source. Similarly, if someone comes across an article for which there are sources they don't know exactly, the template should be added at the very top of the article with the entry {{+source}}.