There's a gravel trail near my house that often has hoof prints on it. While I've seen horses make some of these hoof prints, it's common for me to not have seen the animal that made some particular set of prints.While fair from a point of logical argument, I'd like someone to explain to me how anyone (anywhere) can provide evidence for something nonexistent. I've never once had anyone propose a way in which that can be done satisfactorily, regardless of the topic of god(s).
Judging by the size and shape of the hoofprints, we can say that they're consistent with some possible animals and inconsistent with others. For instance, they're inconsistent with bears, dragons, and people, but they're consistent (as far as I know) with horses, zebras, and unicorns.
Therefore, the hoof prints are evidence for unicorns. They certainly aren't conclusive evidence, but it's conceivable that, given other evidence, that this evidence could be part of a case for the existence of unicorns
... just as, say, the fact that a particular make and model of car was seen speeding away from a crime scene might be an element of the case that some person committed the crime.