Activision has let several game trademarks expire, according to GameSpot. Activision has let trademarks for "Call of Duty: Space Warfare" and "Call of Duty: Secret Warfare" expire. Activision filed the trademark application with the United States Patent & Trademark Office (USPTO) in May 2010, but no game was ever announced.
Activision still holds trademarks for "Call of Duty: Future Warfare" and "Call of Duty: Advanced Warfare," though the company has not announced any such Call of Duty games to-date. Likely it does this from time to time to lock down names that it is strongly considering for use in the future.
The next entry in the series, Call of Duty: Ghosts, releases November 5 on PC and consoles...