bbPress.org

Something like this might work.

Add this php code snippet to your child themes functions.php or add it in a functionality plugin.

function rkk_display_moderator_label() {
    $reply_id    = bbp_get_reply_id();
    $role        = bbp_get_user_display_role( bbp_get_reply_author_id( $reply_id ) );
	
    if( $role == 'Moderator') {
        echo'<div class="bbp-mod-label">Forum Moderator</div>';
    }
}

add_action( 'bbp_theme_before_reply_content', 'rkk_display_moderator_label' );