In my dotnetnet Nuke project, I have to put a sentence in a page for signed (logged in) users. And I have to put another sentence for unsigned users. How can I do this?
You can use the same code that's written in login skin object here: https://github.com/dnnsoftware/Dnn.Platform/blob/30bd1a1bd9d2962a36f6e39403f00ba5877dcfab/Website/admin/Skins/Login.ascx.cs#L84
Visible = (!PortalSettings.HideLoginControl || Request.IsAuthenticated) && (!PortalSettings.InErrorPageRequest() || ShowInErrorPage);
You can only use Request.IsAuthenticated in your case as well.
-- old answer --
Use login skin object provided by dnn to do so.