Sometimes ignorance helps. Not being a regular viewer of The Sopranos, upon viewing the end of the final episode, it appeared very clear to me what it meant. I had no preconceived notions about how the show should or might end, so I just read the events as they occurred.

To me, it indicated that when the screen went black, we were seeing things from TonySoprano’s point of view, and that he had been killed.

It appears that that was indeed producer-writer David Chase’s intention. Reuters reports:

Fans of "The Sopranos" are seizing on clues suggesting the controversial blackout which abruptly ended the TV mob drama meant that Tony Soprano was rubbed out, and HBO said Thursday they may be on to something.

One clue in particular, a flashback in the penultimate episode to a conversation between Tony and his brother-in-law about death, gained credence as an HBO spokesman called it a "legitimate" hint and confirmed that series creator David Chase had a definite ending in mind. . . .

Chase himself suggested as much in an interview Tuesday with The Star-Ledger newspaper of New Jersey when he said of his end to the HBO series, "Anyone who wants to watch it, it’s all there." . . .

The biggest hint, according to a consensus taking shape on the Web, is a scene from an earlier episode in which Tony and his brother-in-law, Bobby "Bacala" Baccalieri, muse about what it feels like to die.

"At the end, you probably don’t hear anything, everything just goes black," Bobby says while they sit fishing in a small boat on a lake.

The Reuters article alludes to an important clue from the series’ final episodes: 

That scene is recalled briefly in a flashback played at the end of the penultimate "Sopranos" episode, as Tony is lying in the darkened room of a safehouse clutching a machine gun to his chest in the midst of a mob war.

"I think that is one of the most legitimate things to look at," [HBO spokesman Quentin] Schaffer said when asked about theories that the Bobby Bacala flashback was meant to foreshadow Tony’s death.