Firstly, it's 'ASR' not 'ARS.' ARS would expand to 'Aero Rifle Survival,' where the actual name of the thing is 'Aero Survival Rifle.'
As for the serial, that's the action, the main tube. It's stamped on the lower right side near the front. So the lower is just a part, something one can swap with no legal issues in the USA nor Canada. Which is important as there are a few lowers required if you're going to be jumping around between .22lr, 10mm, .45" etc.