If you have contest-setter privilege and you want to add news on your contest addressed only to restricted group of users, you can do it by checking an appropriate flag in 'add news' form.
You can check: 'All users' (registered and unregisterd users), 'Logged users' (only registered and logged users),'Problem-setters' (any problem setter will see this news), 'Contest-setters (only author of the contest and co-authors will see this news).
One of the abbreviations (reg/ps/cs) will be visible in the news title.