how to tell diff codes
 

ive searched n not found anything on the subject apart from loking at diff and gearbox charts.
is there a mark on a rear diff to identify what it is, and where on the diff casing is it located?
if not, how do i tell what diff i have in my car just by looking at the diff?

my diff and gearbox are not the originals in my car so i need to verify what rear diff i have installed before i go fitting my dccd controller.