function show_sources() {
     if (!document.getElementsByTagName || !document.createElement ||
!document.appendChild) return;
     var quotes = document.getElementsByTagName("a");
     for (var i=0; i<quotes.length; i++) {
          var source = quotes[i].getAttribute("source");
          if (!source) continue;
          var para = document.createElement("span");
          var link = document.createElement("a");
          para.className = "attribution";
          para.appendChild(document.createTextNode(" "));
          link.setAttribute("href",source);
          link.appendChild(document.createTextNode("(source)"));
       quotes[i].parentNode.insertBefore(link,quotes[i].nextSibling);
       quotes[i].parentNode.insertBefore(para,quotes[i].nextSibling);
     }

 }

• Don't display "Show Sources" link if there is nothing to reveal.
• Don't let the user click it over and over
• improve formatting of the page ( applys to the whole website)