This is already signified in several ways. [list=1][*]In the Forum Display, all threads with new posts since your last visit have an orange envelope. If it has a gray icon, this means there were no new posts.[*]In the thread display, there is a little paper icon next to the time and date of the post. Orange again means it is a new post and gray means it is an old post since your last visit.[*]Clicking on the little blue down arrow next to the thread title will take you directly to the first unread post in that thread. [*]Clicking on the little blue right arrow next to the last posters name will take you to the last post made in the thread.[*]Finally all posts are marked as read after you have been here at the site for 30 minutes or more.[/list=1]
In version 2.0, this is enhanced somewhat. Using session cookies the new post indicator in forum display is changed after you read that thread. Which could make envelopes change more than once during your visit.
You can see what will be in version 2.0 when it is released by visiting
http://beta.jelsoft.com/. However I must say that every feature might not be implemented here and some features will be restricted to Senior Members kind of as a reward.