You can use org-bullets to get nice bullet symbols such as these:

Here is my setup:

(use-package org-bullets :ensure t :init (setq org-bullets-bullet-list '("◉" "◎" "⚫" "○" "►" "◇")) :config (add-hook 'org-mode-hook (lambda () (org-bullets-mode 1))))

You can omit the org-bullets-bullet-list: the defaults look quite nice, too.

If you need inspiration, you can find an exhaustive list of utf-8 symbols here.