How can one add superscript character like TM or Reg on a block title
Block Class Styles may be useful:


  Extends the Block Class module to incorporate styles (or themes)
  rather than css classes. Adds style-based tpl suggestions. Allows HTML
  in your block titles.


Other options would be to create your block in code, and set the $block-&gt;subject to be your &lt;sup&gt; inclusive title, or to override the block-XYZ.tpl.php for the your particular block and add the title in there.

By default, Drupal core runs check_plain on any UI created blocks, so through the UI I don't think there's another option.