Update: Konami also registered "Existence" alone, without a link back to Metal Gear Solid in the USPTO on August 11. "Guns of the Patriots", Metal Gear Solid 4’s subtitle, was also registered separately.
Siliconera reports: Solid Snake's story is finished, but that doesn't mean Konami is going to seal the Metal Gear Solid franchise in an early grave.
The first sign of a new Metal Gear Solid game comes from the Japanese Trademark database where Konami registered Metal Gear Existence with the boring image on the right. It's made to be used with video games so it's likely, very likely, the name of a future Metal Gear Solid game. Going by the title alone it sounds like we're going to visit the existence - or origins of the Metal Gear Solid franchise.