Ordered seeds online

If I were to get a pink slip in the mail would it come as certified USPS mail?

No, lingerie usually ships third class. As for your seeds, you'll either get them or you won't. If customs gets them, they just leave a form letter in the page. Or sometimes a stupid note. If so, just have them resent, providing you got a delivery guarantee.
Customs used green tape to reseal inspected packages, no pink slips.