User blog comment:Master Sima Yi/Assassinews 31-03-'15 — Assassin's Creed Chronicles announcement trailer/@comment-5174994-20150508211258

It seems to be legit that the game is called Syndicate. Kotaku have posted an update (not sure if you guys have seen it) saying this:

UPDATE (5/8, 1:53pm): In addition to hearing the name from other sources, we've seen photos of marketing materials also indicating that the game will indeed be called Syndicate. And the URL on Ubisoft's teaser images says “ACS.”

Considering how much AC news has turned out to be true from Kotaku, I wouldn't doubt that this one also is true.

This is the link to the page if you want to see for yourself.