I am working on a niche news site which has both free articles and articles that require a subscription to read. As far as I know the paid articles will outnumber the free ones.
I want to visually differentiate the paid articles from the free ones in the article listing pages by placing a graphical marker next to them (a lock icon on the paid ones OR a "free" label next to the free ones). But I am not sure which ones to mark.
From a user experience perspective, which option would be better? To mark the free ones or the paid ones?