Dirt 4 teased again by Codemasters14 Feb 2014
Happy Valentine's Day DiRT Fans. We <3 u 4eva x pic.twitter.com/ylqia2bPPe
— DiRT (@dirtgame) February 14, 2014
Perhaps not too conclusive on its own, but it follows several weeks of Dirt lead designer Paul Coleman dropping hints and answering questions about the next installment in the series on his own twitter account.
Finally, the image below appeared on the Dirt facebook page in January. It was neither confirmed or denied as a Dirt 4 shot, but looks pretty rally oriented to me. Plus it has the logo on the side of the car.