My advice, is that if you can't be there to sign for it and you don't have a neighbour that you can authorize to them via the website or whomever you ordered from, is to let them drop the note on your door and go pick it up when it becomes available.
Just trusting them to place it in your back yard, between doors, or just inside is just asking for trouble. You know.. like when you are walking downstairs with soda in one hand and ice cream in the other and you think... hmmm I can carry this bag of chips too, but if I do, I might drop something.. but you don't listen and next thing you know, you are at the bottom of the stairs with both dog and cat cleaning all of the sticky sludge off of you because you tripped on the other pet who had it all cunningly planned. .... I digress but generally if something shows that deep down instinct that it might be a bad idea, it usually is.