Here's another way to add random signatures to Gmail using Google Apps Script. It will update signatures that you store in a Google Sheet at regular intervals. The only problem is… You have to be a Google Apps for Business administrator to run this thing, because the only way to update a Gmail signature programmatically is via the Google Apps fo…

gistfile1.js

function onOpen() {
  var ss = SpreadsheetApp.getActive();
  ss.addMenu("FortunKa", [{name: "Configure", functionName: "doGet"}]);
}

function doGet() {
  var app = UiApp.createApplication();
  var handler = app.createServerHandler("onSave");
  
  var panel = app.createVerticalPanel();
  
  
  var email = app.createTextBox().setName("email").setValue(UserProperties.getProperty("email"));
  var passwd = app.createPasswordTextBox().setName("passwd").setValue(UserProperties.getProperty("passwd"));
  var domain = app.createTextBox().setName("domain").setValue(UserProperties.getProperty("domain"));
  var login = app.createTextBox().setName("login").setValue(UserProperties.getProperty("login"));
  var button = app.createButton("Save").addClickHandler(handler);
  var explanation = app.createLabel("The fortune generator works only for Google Apps for Business administrators." + 
                                    "The administrator email and password are needed to create an authentication " + 
                                    "token for Google Apps for Business Email Setting API. The domain is the Google " + 
                                    "Apps for Business domain. The login is the login of the user whose signature will " + 
                                    "be changed. " + "To set up regular signature updates, go to Resources / Current" + 
                                    "project triggers and setup a time-driven task using the run function.");
  
  
  var grid = app.createGrid(4, 2);
  grid.setWidget(0, 0, app.createLabel("Administrator email:"));
  grid.setWidget(0, 1, email);
  grid.setWidget(1, 0, app.createLabel("Administrator Password:"));
  grid.setWidget(1, 1, passwd);
  grid.setWidget(2, 0, app.createLabel("Domain name:"));
  grid.setWidget(2, 1, domain);
  grid.setWidget(3, 0, app.createLabel("User login:"));
  grid.setWidget(3, 1, login);
  
  
  var panel = app.createVerticalPanel().add(grid).add(button).add(explanation);
  
  handler.addCallbackElement(panel);
  
  app.add(panel); 
  
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  spreadsheet.show(app);
}


function onSave(e) {
 
  UserProperties.setProperty("email", e.parameter.email);
  UserProperties.setProperty("passwd", e.parameter.passwd);
  UserProperties.setProperty("domain", e.parameter.domain);
  UserProperties.setProperty("login", e.parameter.login);
  var app = UiApp.getActiveApplication();
  app.close();
  return app;
}

function getToken(email, passwd) {
  var payload = {
    "Email" : email,
    "Passwd" : passwd,
    "accountType": "HOSTED",
    "service": "apps"
   };
  var params = {
    "method" : "post",
    "payload" : payload
  };

  var response = UrlFetchApp.fetch('https://www.google.com/accounts/ClientLogin', params);
  if (response.getResponseCode() == 200) {
    //Logger.log(response.getContentText().match(/Auth=(.*)/)[1]);
    return response.getContentText().match(/Auth=(.*)/)[1];
  }
  
}

/*
* PUT https://apps-apis.google.com/a/feeds/emailsettings/2.0/example.com/liz/signature

<?xml version="1.0" encoding="utf-8"?>
<atom:entry xmlns:atom="http://www.w3.org/2005/Atom" xmlns:apps="http://schemas.google.com/apps/2006">
    <apps:property name="signature" value="Liz Jones - (+1) 619-555-5555
Accounts Management, A&amp;Z LTD." />
</atom:entry>
*/
function updateSignature(token, domain, login, fortune){  
  var atom = XmlService.getNamespace("atom", "http://www.w3.org/2005/Atom");
  var apps = XmlService.getNamespace("apps","http://schemas.google.com/apps/2006");
  var entry = XmlService.createElement("entry", atom);
  var property = XmlService.createElement("property", apps)
    .setAttribute("name", "signature")
    .setAttribute("value", fortune);
  entry.addContent(property);
  var document = XmlService.createDocument(entry);

  var xml = XmlService.getPrettyFormat().format(document);
  //Logger.log(xml);
    var headers = {
    "Content-type": "application/atom+xml",
    "Authorization": "GoogleLogin auth=" + token
  };
    var params = {
    "method" : "put",
    "headers" : headers,
    "payload": xml
     
  };
  var response = UrlFetchApp.fetch("https://apps-apis.google.com/a/feeds/emailsettings/2.0/" + domain + "/" + login + "/signature", params);
  Logger.log(response.getResponseCode());
  Logger.log(response.getContentText());
}

function getFortune() {
  var sheet = SpreadsheetApp.getActiveSheet();
  var data = sheet.getDataRange().getValues();
  var random = getRandom(0,data.length);
  data[random][0]
  return data[random][0];
}

function getRandom(min, max) {
  return Math.floor(Math.random() * (max - min + 1) + min);
}

function run(){
  var email = UserProperties.getProperty("email");
  var passwd = UserProperties.getProperty("passwd");
  var domain = UserProperties.getProperty("domain");
  var login = UserProperties.getProperty("login");
  if (email && passwd && domain && login) {
    var fortune = getFortune();
    updateSignature(getToken(email, passwd), domain, login, fortune);
  }
}