oracle account in /etc/passwd

I am having trouble getting my scripts to login and run against a 10g database 
on solaris 8.
I can login from the cmd prompt as sysdba all day long.
this is the only entry in /etc/passwd that refers to oracle:
(oracle) $ more /etc/passwd
In /etc/group I see no entries for dba and oinstall.  Oracle and oinstall are 
the software installers and owners.
Again I can login to sql*plus as sysdba with no problem.
What does the +oracle  entry mean in /etc/passwd?
Is it authenticating from some other mechanism?
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