I think a great way to make this easier would be to show the profile picture of the admin user at this place. Also I think the standard CiviCRM logo should adhere to the "Show 'powered by' setting" in civicrm/admin/setting/misc I will create a PR for the later option.
It's because it's using Helvetica font which doesn't have unicode characters - if you can use Deja Vu Sans or another font that has unicode it should work.
IGNORE rest of answer below. As per comments Cesar found that under Administer - Communications - Label Formats you can change the font in there.
You can try to hack CRM/Utils/PDF/Label.php to hardcode ...