where is the form I sign for delivery if I am not there?

Did you check here:

http://store.apple.com/us/help/shipping_delivery

which includes instructions on delivery pre-signing:

The form appears to be part of your order so you will need to follow the instructions and find it.

Hi

Not too sure what you are looking for can you expand? If you after something to leave instructions for delivery's when you know you will not be at home as far as im aware all apple deliveries will require a signature read below

Missed deliveries

Carrier Delivery: If you are not at home when the carrier attempts to deliver your order, the carrier will leave a card. You can contact the carrier directly for a new delivery appointment during working hours at a suitable date and even amend your delivery address.

If your order has passed the scheduled delivery date in your dispatch notification email, please contact Apple Store Customer Service. We will investigate with the appropriate carrier and strive to deliver your order as soon as possible.

Postal Delivery: If you are not at home for a postal delivery or your order cannot be delivered, a card with collection details will be left for you. In most cases, you can collect your order from the Postal Delivery Office where it is being held and you may be able to arrange a redelivery.

You can track your order by clicking Account at the top of the page and selecting Track an Order. If your order is being delivered by the postal service and you have not received it 5 days after dispatch, please contact Apple Store Customer Service.