How do I show if a user has read a record

Hi, this isn't specifically about an issue with your extension, more a query to see if you have an extension that can do what I am looking for.

I've built a forum, and all is working pretty good bar a few little niggles, but I would really like to know how to visually notify a user that there has been a response to a post. Just as this forum does, when a new reply is added to a thread, the text goes bold and an icon appears. Once the user has visited the page, icons are removed and text returns to normal.

What extension do you have that would enable me to achieve this? I have a feeling that cookie toolkit might do it, but I have never used it, so don't know if it's the right tool for the job, or how to implement it if it is.