Index: src/wp-signup.php
===================================================================
--- src/wp-signup.php	(revision 34820)
+++ src/wp-signup.php	(working copy)
@@ -37,6 +37,23 @@
 	die();
 }
 
+$network_site_url = network_site_url( 'wp-signup.php' );
+/**
+ * Filter the signup location for this WordPress installation.
+ *
+ * @since 4.3.0
+ *
+ * @param string $network_site_url URL of the signup page for WordPress.
+ */
+$signup_location = apply_filters( 'wp_signup_location', $network_site_url );
+$signup_location_parts = explode( '?', $signup_location );
+
+// 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;
 
@@ -64,8 +81,14 @@
 	</style>
 	<?php
 }
+add_action( 'wp_head', 'wpmu_signup_stylesheet' );
 
-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();
 
 /**
@@ -91,11 +114,11 @@
 	$current_site = get_current_site();
 	// Blog name
 	if ( !is_subdomain_install() )
-		echo '<label for="blogname">' . __('Site Name:') . '</label>';
+		echo '<label for="blogname">' . __( 'Site Name:' ) . '</label>';
 	else
-		echo '<label for="blogname">' . __('Site Domain:') . '</label>';
+		echo '<label for="blogname">' . __( 'Site Domain:' ) . '</label>';
 
-	if ( $errmsg = $errors->get_error_message('blogname') ) { ?>
+	if ( $errmsg = $errors->get_error_message( 'blogname' ) ) { ?>
 		<p class="error"><?php echo $errmsg ?></p>
 	<?php }