I'm working on a new website for our company that is based on Kentico CMS 4.0 (I haven't upgraded to 5.0 yet). Our site includes many pages that are accessible to anonymous users, but also many pages that are only available to contracted agents who are logged in. Our site has a drop down menu at the top, and most pages also have a tree menu on the left of the page for the current section of the site they are viewing.

So that users will know what pages they can access as a public user, I'd like some kind of visual indicator on the secured webpages. Otherwise, the user may click on the the item in the menu, get blocked by a login page, try another page getting the same result, and get frustrated and leave the site. I don't want to hide the menu items, however, for two reasons:
1. I want to show prospective agents the resources we have available for those who contract with us.
2. I want a contracted agent to be able to select the page they want without first logging in. They'll just get prompted to log in before the website will display that page.

So, essentially, I want to visually differentiate all menu items for pages that require authentication, either by an icon or perhaps a differently styled menu item, if the user isn't authenticated. However, I haven't found any facility for this in the built-in menu controls, and I don't particularly want to write a new set of menu controls from scratch. Does anyone have any suggestions for how I could implement this?