Is this for the forumhome page when there are no new posts in a forum? If it is then I believe that's a phrase, but might be best to check and see if you can edit the template and simply place your desired text there instead of editing a globally used phrase that is pretty generic i.e. "Never" so it could be used elsewhere and by changing "Never" to "No New Post".
If you meant on forumhome the icon legend then you can edit a phrease for that or the template as well.
If you can clarify where exactly on the site you meant w/ a screenshot that will help us, help you

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