@ Bigbull99,
Yeah, because you requested for delivery confirmation, they need someone physically to collect the package. And since they couldn't find anyone at the destination to pick it up, they left a notice so the recipient can go pick the package at the post office address on the back of the notice.
Calm down, there isn't any cause for alarm. USCIS mailman will pick up your package by tomorrow.
Enjoy
Thank you for the info. It helps,
But it sent to a PO Box. I thought they just leave it in the PO Box. I asked the same to the USPS lady on the phone, She said may be the box is full or too small for the package. USCIS get lots of mail every day. I guess they should have a big box.