I just bought a Digitech Jam Man, and I want to register it as well as take advantage of the guitar center "free overdrive pedal" deal. I do need my serial number for at least one of these, their website says to look on the back, unfortunately that's a relative term and well... There are plenty of numbers there and none labeled "serial number"

Any pedal owners capable of pointing me directly at it?
Not that I can see. :\ I'm not even sure if I should be looking at the unit or the packaing, though im guessing unit.
Alright. I've got my Digitech Whammy and my Digiverb in front of me. The Whammy's serial number is clearly stated as "Serial No." on the bottom of the pedal. I'm going to give you some credit and assume that this is not the case with your JamMan.
The Digiverb, on the other hand, is a bit more puzzling: the serial number is nowhere in sight. After reading the manual through a couple of times and carefully scanning the label on the back, I still couldn't find anything. So I lifted the battery cover (under the foot pedal) and...voila. It's listed as "XDVV000............". I assume the letters are just the code for "X-Series Digiverb", as the Whammy's code contains no letters.
I don't know if the JamMan has a similar lifting footswitch, or if it has a battery compartment at the back the way Digitech multi-fx units do, but check for any sort of removal cover. Chances are that the serial number will be underneath it. As far as I can tell, it should be an 8-digit code.