Level-5 has filed a trademark for the as-of-yet unannounced Professor Layton and the Last Specter in the USA, according to Siliconera.
The game had previously been released on Nintendo DS in Japan in 2009 and explained how protagonist Luke came to meet the puzzle solver.
Similarly, last year Level-5 filed a trademark for Professor Layton and the Lost Future prior to E3 before officially announcing it a few weeks later.
It seems likely we'll be hearing more about this at this year's E3. Interestingly Level-5 has also recently opened an office in Santa Monica which will be developing games specifically for a Western audience.