Little is known about the trademark.
Sony might have a new game in the works if a recent trademark in Europe is anything to go on. Dualshockers was one of the first to find the trademark filing and this potential game is currently carrying the title of The Sentinel.
There is almost nothing known about what this title could be. What we do know from the actual filing is that it is indeed being classified as a game and it is apparently going to be carrying some sort of online functionality. Until Sony actually talks about what this game could be, we’re not going to do anything more than just guess.
Is it possible that this is going to be one of the games that will be worked on by the new company that’s going to have a mobile focus? The only thing that was found with a quick Google search is a puzzle game that was first produced in 1986. Perhaps this is a remake of that title. For now, all we really know about The Sentinel is its title.