If you miss a UPS delivery and you need to sign for the package the UPS driver will leave a door hanger on your door where they will say they have been to your address but you was not there and they will return to attempt to redeliver your package.
You can also have the package held at a UPS facility where you can go to the UPS store or UPS facility and sign for and pick up the package.
Or you may also be able to sign the door tag as your signature and the UPS driver can sometimes leave the package in a safe spot.
But if there's no safe spot for the UPS driver to leave your package then they will want you to be there.
But most times I've had no trouble signing a door tag and they would leave the package.
UPS will attempt to deliver a package at least 3 times before the package gets sent back to the sender.