// ==UserScript==
// @id             www.tumblr.com-bc9c68d4-c9f0-4d69-b972-24258720179f@scriptish
// @name           tumblr redirect
// @version        1.0
// @namespace      
// @author         
// @description    
// @include        https://www.tumblr.com/
// @run-at         document-start
// ==/UserScript==
var signup = document.evaluate('//title["Sign up | Tumblr"]', document, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null);

if (signup) {
	window.location = "https://www.tumblr.com/login";
}