If your profile access is set to public, this will be the default option. The notice will be visible to everyone.
If your profile access model is default, you can select account required to make a notice available to all users who have a registered account. This notice will not be shown to everyone.
When you are in a Notice, go to App Options > Advanced. Click Custom.
A window will popup where you can select App Groups, or App Accounts. It is recommended you create a group if you want to give access to more than 10 people.
Start typing the name of a group or account and select the correct group or account.
Save your notice. A notification will be sent only to the select accounts / group, and they will be the only accounts that can access the Notice.