are you sure?
I would say it was a tuner also considering the fact that it's necessary to tune the low E string to D...
Its not a tuner. This Fryer guitar is Brian's permanent drop D guitar and is tuned with his other guitars before the gig. Their is no need for any of his guitars to have a tuner fixed to the headstock. The spare to this guitar is a Guyton. The spare to Brian's main guitar is his other Fryer.
It is in fact a camera, if you watch FBG from Moscow, you can see footage from the camera on the screens across the rear of the stage.