Magento如果声明采购订单

I am trying to write an PHP if statement in magento for order invoices for purchase orders - Basically I want to keep it to say Purchase Order: (#) for most invoices, but for one of my stores instead of PO's they use Co-OP id's well I want to change the invoice to say Co-Op ID: (#) whenever it's a certain store.. here is the line of code that I most likely need to change :

<?php echo Mage::helper('payment')->__('Purchase Order Number/Co-Op ID: %s', $this->htmlEscape($this->getInfo()->getPoNumber())) ?>

and here is the code that I am trying to use for my if statement (I am not sure if this is correct, as I am not a PHP expert nor Magento expert)

<?php if (Mage::app()->getStore()->getName() != "verizon") {

you can get store id directly from this statement in your invoice php file $invoice->getStoreId() and you can make condition base on your store id