(with-eval-after-load 'notmuch
  (setq notmuch-search-result-format
        '(("count" . "%9s ")
          ((lambda (_ thread)
             (concat
              (propertize
               (if (member "unread" (plist-get thread :tags))
                   "*" " ")
               'face
               'notmuch-tag-face)
              " ")))
          ("subject" . "%s"))))