How to set a dynamic title in Cell/header directory in cakePHP 3.0?

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1 
<div id="header">
<div class="header-title">
    <h2><?php echo (isset($pageTitle)) ? $pageTitle : 'Test'?></h2>
</div>
This code snippet runs perfectly and on every page. I am trying to set the $pageTitle dynamically. This means that I am trying to set it for every page differently. I have set inside the UsersController.php $this->set('pageTitle', 'Nebojsa'); In index method. But when I go to the url /users/index , this page title stays 'test'. I have also tried to assign the value inside the Template/Users/index.ctp <?= $this->assign('pageTitle', __('Users')); ?> But it won't work. What am I doing wrong ? Could you maybe point me in the right direction, where should I look ?