Adding a header to a views glossary
You need to be able to perform business logic (php) in your Views header (or footer) to perform this task.

The Views header or footer should be able to accept PHP, just change the input filter to PHP. If that input filter is not available, you'll need to enable the PHP Filter module (core, optional) first.

Once you can use PHP in the Views attachment header or footer you can include logic to look at the selected glossary item such as:

$term = check_plain($_GET['glossary_term');
echo "&lt;div id='selected-glossary-term'&gt;" . $term . "&lt;/div&gt;";


Then use whatever CSS you need in your theme or module to make this Letter appear however you wish.