There is now setting you can configure to do so. But master..syslogins has a column (updatedate) so you could make a job that select every login that haven’t change their password for, let say for a, month.
Select loginname from master..syslogins where datediff(Month,updatedate,getdate())>1
Now you can decide if you make a cursor that change all the password (which givs you the problem too tell users) or you email them ask them to do so.
I think it's master.dbo.sysxlogins which contains a field named xdate2 which is basically the last time the password was changed.But the fact is that there is no other way to do this,unless you email the users about their password expiration.Sybase has a "Sysetmwide password configuration option" which was very useful in defining the serverwide password expiration dyas.