I'd say it means that if there is no God then that's the end of any moral code - as in the need for people to act in a way that is considerate of others etc. This of course assumes that it's only a belief in God that leads people to lead a moral life...which is rubbish.
Atheism is not believing in god, as to permissible is when you just pass it by, so to those who believe in god: in other words; you don't believe in heat even though you can only feel it, then nothing you can't see exist as well.
Atheism is not believing in a god! It does not change any moral code! There are laws that we must obey and this has nothing to do with a god! It is the universal human code! Treat people as you would like to be treated, very simple. A god only exists in the human mind.
It means that sometimes we have to do our own thinking. And that just because some will run wild in the streets and do what the hell ever type of nonsense they want, that you will instead start a God and start doing worthwhile stuff. Like hanging out with folks that aren't justifying selfish acts by tripping on there being no God. And shying away from self righteous folks who do nothing to help while preaching the opposite. Start a God if there is none.