You know the drill by now -- company files trademark, could mean nothing, but we all go crazy because IMAGINE IF IT MEANS SOMETHING ACTUALLY! So yes, Bungie has filed a new trademark for Marathon, its pre-Halo FPS that everybody has fond memories of, but if they played it now they'd probably have a terrible time.
Marathon was released in 1994 on the Apple Macintosh and Pippin and spawned two sequels. The first sequel, Marathon 2: Durandal, was released on Xbox Live Arcade back in 2007. Download that and you can get a good idea of how well it aged (spoiler: not well).
As we said, the new trademark could mean nothing, but it could represent what the chaps at Bungie are thinking of doing next. Would you like to play a brand new Marathon?