Symbolic Code for Delete
There's no symbolic code/constant for 'Delete', no.

The button containing that text gets set in the main node_form() function though:

$form['actions']['delete'] = array(
  '#type' =&gt; 'submit', 
  '#value' =&gt; t('Delete'), 
  '#weight' =&gt; 15, 
  '#submit' =&gt; array('node_form_delete_submit'),
);


and making the assumption that no other module is changing the #value of that variable by way of a form alter, you'll be safe checking the clicked button text by wrapping the same string in t():

if ($node-&gt;op == t('Delete')) {
  // ...
}