How to pre-select "Show blocks" button?

There is a setting for that called startupOutlineBlocks, but there's currently no widgets in the editor profile GUI to change it.
You can however do this in a small module to set it:

/**
 * Implements hook_wysiwyg_editor_settings_alter().
 */
function MYMODULE_wysiwyg_editor_settings_alter(&$settings, $context) {
  if  ($context['profile']->editor == 'ckeditor') {
    $settings['startupOutlineBlocks'] = TRUE;
  }
}

Here's a snippet for Drupal 8.
Pre-selecting the button for all ckeditor enabled formats.

//Pre-select the show blocks button
function HOOK_editor_js_settings_alter(array &$settings) {
  foreach (array_keys($settings['editor']['formats']) as $text_format_id) {
    if ($settings['editor']['formats'][$text_format_id]['editor'] === 'ckeditor') {
      $settings['editor']['formats'][$text_format_id]['editorSettings']['startupOutlineBlocks'] = TRUE;
    }
  }
}

@TwoD

Super Dope!!! Thank you.