Have a look here mate.
Australian War Service Badges WW2
and here for a WW1 example.
AWM Collection Record: REL30389 - Returned from Active Service Badge : Corporal F McArthur, 13 Infantry Battalion, AIF
I'm not 100% sure but the number wouldn't be his service number but the number of the badge awarded to him.
His details would be recorded against that number.
I'm open to correction.