You can check check in your templates in which your product object is available for the
taxClassId stores the information about the tax class assigned to a product for example in admin panel.
taxClassId = 0 means the product has no tax class,
taxClassId > 0 means the product has a specific tax class.
For example you can use the following code in
$_vatSuffix = '';
$_vatSuffix = ' +VAT';
<?php echo $_coreHelper->formatPrice($_finalPriceInclTax, false) . $_vatSuffix ?>
This is only an example to show, how you can identify the products with VAT and based on that information add a price suffix. You will have to change some other templates depending on your theme and customization.
I hope that helps.