Stolen Mail?

[Yin]

A package of mine was signed for. It was sent usps and tracking number says it's been delivered. I never received it, could it have been stolen? I can't check my mailbox because I don't have a key. Could it be at the post office? The main thing that makes me think this is because it says it was delivered and signed for. Am I worrying too much? If it's in the mailbox, I can just wait by it with an ID, but if not then... Is it lost?