What I see as evidence for God's existence would be denied by a non-believer but that's why it's called faith. I have faith that there is a God. Sometimes I have doubts; often I question. But I believe. But I'm not sure I'm certain. At least I don't have the sort of assurance that the writer of this lamppost sticker seems to have.
And I can't quite put my finger on it but there's something wrong with the logic too. Is it suggesting you stop worrying about whether there's a God or about what you do? In either case my experience is that my belief in God means I can enjoy life.
Or am I just taking a lamppost sticker too seriously?