WordPress at a glance
function is not described

do_signup_header() WP 3.0.0

Prints signup_header via wp_head

Hooks in function
Return

Nothing (null).

Usage

do_signup_header();

Code of do signup header: wp-signup.php VER 5.0.3

<?php
function do_signup_header() {
	/**
	 * Fires within the head section of the site sign-up screen.
	 *
	 * @since 3.0.0
	 */
	do_action( 'signup_header' );
}