Board Thread:Warhammer 40k General Discussion/@comment-58.178.141.62-20140405080514/@comment-173.79.234.217-20140405185525

Besides the prophecy of a raven crying tears of blood for its lost primarch, Black Library has a loyalist Thousand Sons guy show up in a short story and then a novel later on (along with around 1,000 other loyalists.  Coincidentally just enough for a chapter...) with a similar name to one of the most famous blood ravens, who had a raven motif, and who used the Blood Ravens quote "Knowledge is power". And he's still active in the story (of the Horus Heresy) since he had a pretty decent-sized role in Scars, which is a relatively recent Horus Heresy novel.

It honestly doesn't get much more obvious than that beyond a direct explicit statement. As in, there is practically literally nothing more they could currently do at this point in the plot short of an author blurting it out directly to imply he's the founder of the Blood Ravens.