The syndication-source tag was a tag that became defunct in 2011. Google now recommends that web publishers block crawlers from indexing syndicated content.
In 2010, Google introduced two new meta tags for news articles: syndication-source and original-source. These tags were designed to enable news curators to publish another site’s article on their own site, without risking a Google penalty for duplicate content or plagiarism.
Syndication-source marked an article which was a close or exact copy of an article on another site — the original. Google was then able to pass credit over the original article URL and feature it in Google News instead of the copy.
<meta name=”syndication-source” content=”http://www.heard-it-here-second.com/story.html”>
The original-source tag enabled Google to identify the original news story and reward the site by featuring it on the News search results page. An article using information from many other articles could feature several original-source tags, to pass credit over to their research sources.
<meta name=”original-source” content=”http:///www.breakingnews.com/latest_story_1.html>
Duplicate content issues were avoided using these tags until 2011, when the rel=canonical tag was introduced as the preferred alternative.
Late in 2011, Google announced that the rel=canonical tag (which performs a similar job to the original-source tag) had become the preferred method of indicating duplicate and original content.
Then in 2012, the Google News team stated that the syndication-source tag had been depreciated and that resolving duplicate content articles then hinged on rel=canonical and ‘disallow’ or noindex meta tags.
In 2023, Google updated their guidelines once again. Because pages that copied syndicated content were often quite different to the original source material (i.e. web publishers will often copy a huge chunk of an article, but they will still write a small amount of additional text when uploading it to their site), the canonical tag is often ineffective/sub optimal. Google now suggests using noindex or disallow to prevent the indexing of syndicated content full stop.