NX-OS doesn't offer a separate security version. It looks like this is (another) one of those things you can't do with NX-OS like your were used to with IOS.
If you have syslogging turned on, you will see any instances of a user entering configuration mode:
2012 Nov 3 13:27:23 %VSHD-5-VSHD_SYSLOG_CONFIG_I: Configured from vty by on @pts/0