We do not require a signature upon delivery. However, FedEx can require a signature in certain areas due to high rates of theft or missing packages regardless of the shipper's preferences.
You can create a free FedEx Delivery Manager account to authorize shipment release and give permission to the driver to deliver your package if won't be home to sign in person. Alternatively, you can leave a note on your door for the driver, in hopes they will abide by that.