I wouldn't sign it. This is not common at all, and while it's probably not enforceable, you don't want to chance it. It's interesting that they have told you th

I wouldn't sign it. This is not common at all, and while it's probably not enforceable, you don't want to chance it. It's interesting that they have told you that this is common in Silicon Valley because California has restrictions on requiring employees to assign rights to work created on their own time.