Ok now for my take one this. The Fed-ex requires that the box be marked "live harmless reptile" in at least two place if I remember correctly. Depending on the state you are shipping to you have to even put something stating the species and quantity in the box. I do this for all my shipments because I'm never sure what states the package will be transported through and how or what that area will require, it's as easy as a $.02 address label.
Requesting a signature is one of three ways, 1: addressee only, 2: Adult signature, 3: Signature. When I will normally pay the 2-5.00 extra to have third party electronic verification when and that the package was received. This can in handy recently when I shipped a Mojo to someone and they happened to be in school at the time the animal was delivered. I requested that it be a direct signature. I get notice that it was delivered but no word from the buyer that everything was A-OK. 4 hours later I find out that it was his brother that signed his name and had just thrown the box is his room. Luckily the animal was fine and the customer was happy. Had it turned out for the worse then I'd of had to go to Fed-ex and start an investigation.
If the shipper is worth their salt the package the snake for a 30-48 hour stay in the box knowing that it will not be in there for more than 24. Shipped a snake a couple of year that due to weather the animal sat in Memphis for a full 24 hours. It arrived just fine and ok due to me packing if for a 48 hour trip instead of a 12 hour trip.
In closing it's all in the shipper and their diligence to good shipping practices.