Here's the teaser from Game Informer:
"Usually, we like to reveal the name and final cover art for our upcoming issue's cover story the Thursday before it hits subscribers. This time we're saving the full unveiling of the game's title until Monday during Microsoft's E3 press conference, but we can confirm that our next cover is the new installment in the Gears of War series and is coming to Xbox 360. We figure this news and a glimpse of the shrouded Gears of War cover are least some consolation, as the image raises some interesting questions: Who is in chains, and where?"
Perhaps this hints at a prequel for GOW? Chains could be a reference to Marcus Fenix being found to be a prisoner at the start of the original game.
Meh, I doubt a prequel for Gears would be THAT interesting as there's not such a massively wonderful backstory unless you count Emergence Day etc.... I have pondered the GOW prequel matter before if you're interested.