I would assume no effect (unless the rider was a SMC).
Motorcycles are shot at as if the target was just infantry:
D15.5 TARGET STATUS: Fire is directed at the Rider of the motorcycle - not at the motorcycle itself and therefore does not cause any Collateral Attack or Immobilization result. Motorcyclists are considered an Infantry Target Type with no Target Size modifier. However, all fire vs a mounted motorcyclist is subject to a -1 To Hit DRM for ordnance or a -1 IFT DRM for non-ordnance weapons.
Thus, your Sniper dr2 would result in a Pin result versus an MMC, which is NE for motorcyclists:
D15.54 PTC: A Pin result has no effect vs a motorcyclists so PTC are not resolved vs them...
However, if your rider was a SMC, he would be wounded by the shot, though he wouldn't have to bail out:
15.56 WOUNDS: A motorcyclist which is wounded suffers no additional effects and may continue movement with his normal four MF allotment (A17.2). He does not have to Bail Out or dismount.