To show the theme Logo:
<a href="<?php echo $this->Html->safe($this->base_uri);?>">
<?php if (!empty($theme_logo)) { ?>
<img src="<?php $this->Html->_($theme_logo);?>" alt="Logo" />
<?php }else{ ?>
<img src="<?php echo $this->view_dir;?>images/logo.png" alt="Blesta" />
<?php } ?>
</a>
To show a custom logo:
<a href="<?php echo $this->Html->safe($this->base_uri);?>"><img src="urltologo.png"></a> or
<a href="<?php echo $this->Html->safe($this->base_uri);?>"><div class="logo"></div></a> or
<a href="<?php echo $this->Html->safe($this->base_uri);?>" class="logo"></a>