WordPress Multisite : how to remove access to signup page

If you use WordPress Multisite and want to remove access to signup page, you can add this code to your plugin or function file to redirect visitors to home page:

<?php
/*
* WPMU Multisite - block access to sign-up page
*/
add_action( 'signup_header', 'wpster_prevent_multisite_signup' );
function wpster_prevent_multisite_signup() {
	wp_redirect( site_url() );
	die();
}
?>