Wow. It looks like the CA DOJ has modeled their "assault weapons" guidelines off of the NFA. Engraved with a CA specific SN? That is insane. 
This is exactly the type of thing that gun owners complain about regarding gun control legislation - it NEVER ends. You may have been legal during the last two assault weapon bans, and even complied with the ridiculous requirements like the gun being on the "safe to own exclusively in CA list" and the bullet button ban rendering mag changes impossible without a tool but ... how about "featureless" rifles? .... but .... engraving!!  

and there is NEVER and end to the anti-gunners' "but..." part. There will always be one more thing. 

Anyway, here is a link to well-written article which also includes a picture of the new application: 
https://bearingarms.com/beth-b/2017/05/19/breaking-ca-assault-weapons/?utm_source=badaily&utm_medium=email&utm_campaign=nl&utm_source=badaily&utm_medium=email&utm_campaign=nl