Killzone publisher Sony Computer Entertainment dropped a teaser image on the series' Twitter account today, with the image accompanied by nothing but the word "soon."
Killzone: Shadow Fall (screenshot above), the PlayStation 4 launch title, was the most recent full game in the Killzone franchise. Last August, Guerrilla Games released a stand-alone version of Killzone: Shadow Fall Intercept, a co-op expansion for the first-person shooter.
Today's teaser image could signify something involving Killzone: Mercenary, which Guerrilla Cambridge released on PlayStation Vita in September 2013. The eyes of the Helghast helmet in the artwork, which you can see below, feature the symbol for the currency that players earned in that game.