How can I tell if my O-gauge Lionel train set is pre-war or post-war?

[plainswalker]

I believe it is pre-war, because my father bought it used in 1947. I have an engine, coal car, 2 passenger cars, and a caboose. The passenger cars have lights inside and as I recall, you can do something to get the engine to puff smoke out of the stack. Thanks for your help!