MetaExtension license:uri
Is used to to define the uri to the license, under which a website is published. This can either be your own license, which you've uploaded on a server, or an official source, such as the CreativeCommons-website.
Please note: Only use license:uri if the license you are willing to use is not already listed as a content-possibility in license.
Usage
<meta name="license:uri" content="https://creativecommons.org/licenses/by-nc-sa/4.0/">License URIs for content may be:
- GNU-AGPLv3 (opens in a new tab)
 - GNU-GPLv3 (opens in a new tab)
 - GNU-LGPLv3 (opens in a new tab)
 - Mozilla-Public-2.0 (opens in a new tab)
 - Apache-2.0 (opens in a new tab)
 - MIT (opens in a new tab)
 - Boost-Software-1.0 (opens in a new tab)
 - The-Unlicense (opens in a new tab)
 
Also see license.