A phrase that is use to state something that is already apparent, but in order to draw additional attention to it. Used for dramatic effect, or to emphasize an important point. It is said in a loud manner, at the beginning of a sentence, followed by the fact that needs additional attention.
Popularized by Antoine Dodson, who used the phrase to increase awareness of the fact that there was a rapist in his neighborhood.
Since that time, use of this phrase has been increasing, and it can be used at any time, when an obvious fact needs to be pointed out.
"Well, obviously, we have a rapist in Lincoln Park." - Antoine Dodson
Other examples in common speech:
Janine: What happened to my money I left on the bar?
Bruce: Well, Obviously, we have a thief in Snuffy's Bar.
Janine: Oh wait, I spent it all on wine.
Bruce: Well, obviously, someone has drank too much.