Back on SR1 I ordered some suboxone strips from a major vendor who mostly dealt heroin, and in fact one who was busted eventually and had mainstream media and vice.com articles written about them.
If you've never had subs the paper thin sub-lingual strip is packaged inside a paper thin foil wrapper. Easiest thing to ship stealthily.
My order came in a plain white envelope, but the vendor had used a stamps.com account to print the postage and label! Stamps.com accounts allow you to print barcode postage at home instead of a stamp, and the account is tied to a name and social security # and credit card. I know since I sold on ebay and had one.
All LEO would need to do is order once from said vendor, then get not only all the sellers info from the postal service but also the info on every customer who ordered and had their postage printed.
What is the worst you've seen?
I got a non-scheduled prescription from India, and the dude wrote the drug name on the fucking package, and I got it. I did have to sign though. Maybe customs just felt sorry for me :/
A package of dried poppy pods from UK that was in a sketchy brown package with only one vac seal.
I hate the dvd case too...