My opinion as a GM only; I'd work with my players on this. If someone wants a hidden weapon mount on his Roadmaster, null sheen. On a Suzuki Mirage, it becomes more about what type of weapon; anything up to SMG, sure, why not. Larger than an SMG and you're looking at a weapon that would take up a lot of space in a small bike. While a Harley-Davidson Scorpion CAN take a heavy weapon mount (or two standard weapon mounts) I find it hard to believe that you could successfully conceal a machine gun (or two assault rifles) within the body of such a bike, so to my mind those would be external weapon mounts.
Most drones would require external mounts as I see it; the ubiquitous Roto-Drone (now made redundant by the F-B Bumblebee) seems like it would be a hard sell for internal weapon mounts.