Looks for Pivotal Tracker story ids anywhere on github.com. Any string that looks like: "#12345678" will have a link inserted to the corresponding pivotal tracker story. Don't worry, this will not interfere with github issues, until the ten millionth issue.

gitpivotal.user.js

// --------------------------------------------------------------------
//
// ==UserScript==
// @name           Let's Git Pivotal
// @namespace      uk.co.deliveroo.labs
// @version        0.4
// @description    Looks for Pivotal Tracker story ids anywhere on github.com. Any string that looks like: "#12345678" will have a link inserted to the corresponding pivotal tracker story. Don't worry, this will not interfere with github issues, until the ten millionth issue.
// @include        https://github.com/*
// ==/UserScript==
"use strict";
var regex = /#[0-9]{8}/g;

function addPivotalTrackerLinks(element) {
  var pivotalMatches = element.innerHTML.match(regex);
  var innerHTML = element.innerHTML;

  for (var i = 0 ; i < pivotalMatches.length; i++)
    innerHTML = insertLink(innerHTML, pivotalMatches[i]);

  element.innerHTML = innerHTML;
}

function insertLink (innerHTML, pivotalStory) {
  var id = pivotalStory.slice(1);
  var link = '<a class="issue-link" href="https://www.pivotaltracker.com/story/show/'+id+'" target="_blank">'+pivotalStory+'</a>';

  return innerHTML.replace(pivotalStory, link);
}

addPivotalTrackerLinks(document.body);