A stock version of the Western Motorcycle Company Sovereign, a street bike returning from earlier HD-era games, is due to appear in Grand Theft Auto VI. It is seen in red with a girl leaning against it at the Stockyard car meet in the first trailer, presented as a Sovereign stripped of its usual paintjob and rear top box, and it appears to serve as the base model for several variants including a police bike.
Vehicle data via GTA Wiki (Fandom), CC BY-SA 3.0.