How to check if CUA is used

1) How do we know if Central User Administration (CUA) is used in a system?
 
>You can quickly run transaction SU01 and see if the "Systems" tab is available. If it is then CUA has been configured.
>Well there is another way to see whether CUA is used. Run transaction code SCUA to see if there are any distribution models defined. 
>Run transaction code SCUL to see to view logs that are generated by CUA & if you have logged into a child system, then goto transaction code SU01 and see, there will be no CREATE activity.