Danny
I am (seriously) convinced that there is an exhaust trail in the wake of that model, but you're right about the brown pennant. The model has a broad beam for its length, suggesting a hydroplane type hull? Looking at the wake, the model had just turned to Port. The length of the wake suggests that it's moving quite quickly.
It would be easier to see the pennant with the aerial fully extended, but as the aerial is only extended to four sections, the pennant is partially in the shadow of the guy's left ear.
Malc