Hi @jsprfrmn,

By default, wpForo allows showing signatures for at list first level of reputation (1 star). By default, it's 5 posts. This is another level of spam protection. As far as I see, this user has only 4 posts. His signature will be displayed in one post.

If you want to remove this limit, you should put this hook code in either a PHP code snippet of Code Snippets plugin or directly in the functions.php file of your current active theme:

add_filter('wpforo_min_rating_level_for_signature', 0);