NeoGAF forum member Rosti has done a bit of digging and discovered some exciting news: Sony has recently trademarked two new names.
These is no other information on these games so far other than the names: Entwined and Kill Strain. In fact, they might not even be for the PlayStation 4 at all but rather for the PlayStation Vita, but given Sony's push for new IPs for the PS4 it seems likely this is where the games will end up.
It seems very likely we will see both of the games revealed at E3 as part of Sony's press conference, which has historically always focused on games.
Update: Sony has recently filed two additional trademarks for games: Guns Up! and Bloodbourne. No information on the system or what kind of game these will be, but we do know E3 is shaping up to be an exciting time for PS4 fans!
Update 5/8/2014: Anonymous sources are reporting that "Kill Strain" is going to be a Syphon Filter reboot for the PS4. Syphon Filter was one of Sony's premier franchises during the PS1 and PS2 era but has laid dormant for years. The rumors indicate the game would be called Syphon Filter: Kill Strain.
Article by - Joshua Phillips
Insert Date: 4/22/2014