It's completely your preference in which way it's mounted; it can be frontwards or backwards.
With it backwards, it provides some small measure of protection compared to "frontwards"; the chain is further inboard and away from you but your pants leg is more apt to get caught in the teeth if it's mounted frontwards.
To be serious though, you should have a chain/clutch guard to cover all those moving parts up--unless you like to live dangerously.
