How to implement apple-touch-icon to a site
I enhanced @willtate code a little.
Note: If you need to create the icons quickly use this online generator: http://iconifier.net/

Add the default icon

$apple_icon =  array(
  '#tag' =&gt; 'link',
  '#attributes' =&gt; array(
    'href' =&gt; path_to_theme() .'/apple-touch-icon.png',
    'rel' =&gt; 'apple-touch-icon-precomposed',
  ),
); 

drupal_add_html_head($apple_icon, 'apple-touch-icon');


Loop through to add various sizes

$apple_icon_sizes = array(57,72,114,144);

foreach($apple_icon_sizes as $size){
  $apple = array(
    '#tag' =&gt; 'link',
    '#attributes' =&gt; array(
      'href' =&gt; path_to_theme().'/apple-touch-icon-'.$size.'x'.$size.'.png',
      'rel' =&gt; 'apple-touch-icon-precomposed',
      'sizes' =&gt; $size . 'x' . $size,
    ),
  );
  drupal_add_html_head($apple, 'apple-touch-icon-'.$size);
}


HTML Output

&lt;link sizes="57x57" rel="apple-touch-icon-precomposed" href="sites/all/themes/yourtheme/apple-touch-icon-57x57.png"&gt;&lt;/link&gt;
&lt;link sizes="72x72" rel="apple-touch-icon-precomposed" href="sites/all/themes/yourtheme/apple-touch-icon-72x72.png"&gt;&lt;/link&gt;
&lt;link sizes="114x114" rel="apple-touch-icon-precomposed" href="sites/all/themes/yourtheme/apple-touch-icon-114x114.png"&gt;&lt;/link&gt;
&lt;link sizes="144x144" rel="apple-touch-icon-precomposed" href="sites/all/themes/yourtheme/apple-touch-icon-144x144.png"&gt;&lt;/link&gt;
&lt;link rel="apple-touch-icon-precomposed" href="sites/all/themes/yourtheme/apple-touch-icon.png"&gt;&lt;/link&gt;