Did the package have to cross any borders? If it had to make it by customs they do open random packages but they will leave note saying it had been opened and inspected and if they took anything. They also have special tape to reseal...anyway its quite obvious
When I ordered a package before, it had a big red sticker on it saying "INSPECTED" and a letter inside saying it was for a security check.
OP, maybe you should send a quick email to the company you ordered it from.