I think your best bet would be to call FedEx and ask them to answer for this oversight in service. You're right, with any purchase over $750 CAD sellers are supposed to get a signature in order to be eligible for Seller Protection through paypal.
At the very least, FedEx should refund the shipping you paid as a goodwill gesture. In the meantime, keep your fingers crossed that the lack of a signature doesn't become an Item Not Received issue for you. If it does down the road, you'll want to save all your paperwork and notes and I mean ALL of it to give to paypal to show you that this was FedEx's mistake and not yours. They may have mercy on you. Also, you'd need it for any claims against FedEx if your buyer didn't get it. Has your buyer said anything? Don't bring the lack of a signature to their attention.
Now, when you say 'direct' you realize you can't write in that box a checkmark yourself, right? It has to be a service you paid to receive in advance when you buy the label and then print it online. Assuming you did so here and not at a Fed Ex office. The label prints it with its own checkmark, you can't write it in pen. I just thought I'd mention that, don't take it the wrong way.
