How would I add markup inside of page title input?
Install HTML Title. It will solve your issue.


  Drupal node titles are restrictive and do not support italicized text
  or superscript text (e.g., Book titles, trademark symbols). The HTML
  Title module allows a limited set of HTML markup (em, sub, sup, b, i,
  strong, cite, code, bdi, wbr) to be used in node titles.


Also take a look at Stack Overflow question HTML\rich text in Drupal's node title?.