How to add a class to a form element in buildQuickForm?
John - There's an existing pattern for simply add the markup to the template for cases like this, and I think it's fine for this situation. So in Register.tpl, just add this markup after the label:

&lt;span class="crm-marker" title="{ts}This field is required.{/ts}"&gt;*&lt;/span&gt;


Note that there was evidently some spots where this technique was used / but then removed in that file (see line 47). I think we can remove that {capture} statement at this point and just put the markup where it's needed.