Actually, something like this is in the works right now. Although it's not inherent in the Linchpin News App.
Atlassian Partner bitvoodoo has an app called "Viewtracker". This app already has the ability to tell whether you have read a news article or not. Right now, we are implementing a visual indicator that conveys this information, so you can see which news items you have read and which ones you haven't. Of course this will only work if you use Viewtracker.
The functionality will be available early in the new year if all goes as planned.