Actions

Functions.php
// Add some text after the header
add_action( '__after_header' , 'add_promotional_text' );
function add_promotional_text() {
  // If we're not on the home page, do nothing
  if ( !is_front_page() )
    return;
  // Echo the html
  echo "<div>Special offer! June only: Free chocolate for everyone!</div>";
}<br>

header.php
do_action ( '__after_header' )