Index: src/wp-signup.php
===================================================================
--- src/wp-signup.php	(revision 35026)
+++ src/wp-signup.php	(working copy)
@@ -37,6 +37,14 @@
 	die();
 }
 
+$signup_location_parts = explode( '?', network_site_url( 'wp-signup.php' ) );
+
+// Redirect to the true signup location if the URL differs from default.
+if ( $signup_location_parts[0] !== $network_site_url ) {
+	wp_redirect( $signup_location );
+	exit;
+}
+
 // Fix for page title
 $wp_query->is_404 = false;
 
@@ -66,6 +74,12 @@
 }
 
 add_action( 'wp_head', 'wpmu_signup_stylesheet' );
+/**
+* Fires just before the site sign-up header.
+*
+* @since 4.4.0
+*/
+do_action( 'before_signup_header' );
 get_header( 'wp-signup' );
 
 /**