I figured out the problem: You must specify an ID in the add_menu array if the title is not alphanumeric. So, this code worked:
function my_admin_bar_menu() {
global $wp_admin_bar;
if ( !is_super_admin() || !is_admin_bar_showing() )
return;
$wp_admin_bar->add_menu( array(
'title' => __( '#'),
'id' => __( 'my_menu_item'),
'href' => admin_url('myurl.php')));
}
add_action('admin_bar_menu', 'my_admin_bar_menu');
The only change is the addition of the line containing ‘id’.