What would you consider to be evidence for God?

[Whateverist]

The problem with this is that there's no way to demonstrate that what is known is independent of the nature of the knowers.  We're all human and so we may share certain cognitive realities that are universal within the species, but yet are not truly universal.  We can't be sure that mathematics is independent of the nature of the knower, so we can't simply conclude that it is objective.  This is a systematic flaw with your definition of objective when applied to concepts.

Any other definition undermines the notion of true objectivity. At best all that remains is intersubjectivity. In my opinion that approach severs the relationship between first principles and external reality.

Then again, if intersubjectivity best describes the best we can do, then your notion of true objectivity would actually be false.