See Where External Files Originate

If Salesforce Files Connect is set up for your organization, Salesforce1 mobile browser app users can see if files originate from outside sources, such as Microsoft® SharePoint®.
Files Connect available in: Enterprise, Performance, Unlimited, and Developer Editions

In feeds and Files list views, external data source names appear below file names. For example, if a file originates from a SharePoint data source an administrator named “Office 365,” that appears below the file name.

Screenshot of a Connected File in the Feed

This information appears only if your organization is set up to reference external files, rather than copy them. For details, see Set Up Salesforce Files Connect.