http://www.imfdb.org/w/images/6/6e/M203a2.jpg
That is
not an M203A2. The A2 mounts to the barrel of the M16 and M4, just like both earlier versions. You can clearly see in the following pics that it has a barrel clamp and no sign of RIS attachment points.
http://cdn0.wn.com/pd/a2/86/a1512110...53e_grande.jpg
http://image36.webshots.com/36/6/66/...1XWAojJ_ph.jpg
http://i52.tinypic.com/zsu6py.jpg
The only difference between the M203A2 and the original M203 is the barrel clamp. The A2 uses a quick release barrel clamp (which originally found its way into the military supply chain via the short-barreled M203A1), the original used a more permanent clamp attached by hex nuts, as seen in the following pics.
http://media.defenseindustrydaily.co...Carbine_lg.jpg
http://i168.photobucket.com/albums/u...-Brad/M203.jpg