Seth Godin advocates using cookies to distinguish between new and returning visitors to your website:
“One opportunity that’s underused is the idea of using cookies to treat returning visitors differently than newbies. It’s more work at first, but it can offer two experiences to two different sorts of people.” (Source: In the Middle, Starting)
Using What Would Seth Godin Do plugin you can implement Seth Godin’s idea. After activation the plugin will show a small box showing text “If you’re new here, you may want to subscribe to my RSS feed. Thanks for visiting!” above each blog post to your new visitors and after 5 visits the message will get automatically disappeared.
The plugin allows you to edit the message and you can add your words to it. You can also customize its lifespan and its location, if you like you can execute the message from some pages.
Other than this it also allows you to specify another message for return visitors.