// ==UserScript==
// @name        AoPS Logout Guard
// @namespace   math_explorer
// @include     *artofproblemsolving*
// @version     1.1
// @grant       none
// ==/UserScript==
 
var ts = document.getElementsByTagName('a');
for (var i = 0; i < ts.length; i++){
  var t = ts[i];
  if (/mode=logout/.test(decodeURI(t.href)) && t.parentNode.id !== 'top-actions') {
    var s = t.href;
    if (s.length >= 24) s = "..." + s.substr(s.length - 20, 20);
    var newElt = content.document.createElement('span');
    newElt.textContent = "[LOGOUT? " + s + "]";
    newElt.style.verticalAlign = 'sub';
    newElt.style.backgroundColor = '#f00';
    newElt.style.color = '#fff';
    newElt.style.fontSize = '75%';
    t.appendChild(newElt);
  }
}

• Changed regex to strictly match mode=logout (I was having problems with perfectly OK links that contained the word "logout" in them)
• Changed String.match(regex) to RegExp.test(str)