[akgt]

Im looking for a option to able to add a Unread Posts icons to each topic like in phpbb and mybb.

[xmasons]

Perhaps this is what you require – bbPress Unread Posts

https://wordpress.org/extend/plugins/bbpress-unread-posts/

[zilveer]

As @xmasons mentioned above you could use the plugin
https://wordpress.org/extend/plugins/bbpress-unread-posts/
for that purpose.
YOu can set the background image for the unread posts and put there an icon.
Do you have CSS knowledge?
regards