Well, very basically, it must be objective.
If you will allow me a small example-
In 1915, the general relativity theory was put forth by Einstein. Part of this theory spoke of "curved space".
The objective evidence for this came in 1919 when it was actually shown, during an eclipse, that the light from distant stars was bent as it passed by the sun, thus objectively demonstrationg what GR had predicted. It is considered objective due to the fact that anybody can look at this evidence and plainly see the effects of curved space.
So the evidence presented must be objective.
Likewise, the evidence must point to the existence of the Christian God, as opposed to evidence that may point to a general "deity".
Although, I'll admit that Id be impressed with any objective empirical evidence that points to any deity at all (yours, mine, or even a member of a polytheistic pantheon)
A touch of parsimony helps as well
Let's start there and see where we go, shall we?