Searching for the right terms you can see how Google (or any other web search engine) can show admin pages, such as Control Panel or Site Admin, as entries in their list of results.
Even when trying to access to them is going to take us to login page, this might not be desirable.
Environment
Liferay DXP
Resolution
As it is explained by Google in this article the solution might be using noindex meta tag in those pages you don't want to be linked.
In order to do so, one possible solution is to create your own Admin Theme based on the one provided by Liferay and then include noindex meta tag in every page.
Then, you need to modify portal_normal.ftl template which renders <head> element to add noindex meta tag.
And that's all, once this Admin Theme is selected as Default Admin Theme, all your Control Panel and Server Admin pages would include noindex meta tag.
