FOR THE FORUM LIST:
There is a NEW POST INDICATOR on the left side of each forum title that can be customized for "new posts" and "no new posts"
**These are the only icons used to indicate when new posts are in the forum group, or no new posts within the category list.
\images\general\ [IMAGE-SET-NAME] \newposts.gif
\images\general\ [IMAGE-SET-NAME] \nonewposts.gif

There is a feature to show "Show Total # of Unread Posts Per Forum" as (XX) next to the forum Thread count.
This feature can be enabled within Control Panel > General > Category & Forum Page Settings: Show Total # of Unread Posts Per Forum

It can be customized within the Style Editor (per each custom style) in the "Category/Forum Properties" group:
.newtotal, add:
font-weight:bold;
**This will control the display style only of the new item indicator on the CATEGORY/FORUM LIST.

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FOR POST LISTS:
Similar to the setting above, there is one to indicate Unread Replies per post, within the POST LISTING.
Control Panel > General > Forum Display Settings group: Show Total # of Unread Replies in Topics
This is controlled by the same Style as previously mentioned.

Unlike the forum/category list, the post list items can be customized on a granular level through the style editor. The entire cell can customized (per each custom style) in the "Post List Properties" group:
.new-topicviews & .new-alt-topicviews, add
font-weight:bold;
**This will control the display style of new items cells on the POST LIST.