Valve has filed a trademark for Half-Life 3, suggesting work on the game could finally be underway.

The trademark was filed by Valve with the EU's Office for Harmonization in the Internal Market last Sunday, September 29. The application is still under examination by the OHIM until being approved.

The news was followed by reports that Valve's User Picker software - an internal database allegedly used by the developer to keep track of projects - was made visible to the public.

The database, which has since been taken offline, was said to reveal that 46 members of staff were working on Half-Life 3 and another 10 on 'Half-Life 3 Core'.

Left 4 Dead 3 was also listed in the database.

While Valve could have registered a trademark to simply protect its intellectual property, the revelation of User Picker is the biggest indication yet that the company is working on the highly anticipated sequel.

Half-Life 2 launched almost a decade ago in November 2004, with smaller projects Half-Life 2: Episodes One & Two releasing in the years that followed.

Since Half-Life, Valve has gone on to develop the Left 4 Dead, Portal and Dota series. Its next title has yet to be officially announced.