First: It's none of your business.

Second: It's impossible to distinguish a 'marijuana cigarette' from a hand-rolled tobacco cigarette through a window.

Third: Calling 911 will have no effect, because your report does not constitute probable cause for police to search him or his home.

Fourth: The police will not even come, for the above reason, and you will certainly be able to hear the note of irritation in the voice of the dispatcher, as he/she is fielding your time-wasting call.

Fifth: Consider that the INSIDE of your neighbor's home is in no sense 'your neighborhood'. If he were smoking marijuana out on the street, or selling it off of his porch, that would be a different matter.

And finally: Yes, trouble could come to you from making unfounded reports to law enforcement. Not only will the police themselves be very, very irritated with you, but if you were to do it repeatedly your neighbor could sue you for harassment, and win.

ps- Looking into your neighbor's windows is a nasty habit indeed, even if only a glance.