This is one of those tough signs to value CJ. As a Mobil collector, I would not be interested in buying a sign like this, due to the obvious damage and especially the missing part. I would much rather spend my money on a complete sign with minimal damage, limited to some chips here and there, especially at the legs and tail where damage is common on this particular sign.
Is it worthless...? Heck no, someone out there would buy the sign as is, but as such it only appeals to a limited number of buyers. Like DB mentioned, someone who isn't condition conscious could throw it up on the wall and hide the rear legs, and no one would know but the owner. I'm curious if you are looking for a value to sell it or just to see if you paid a decent price for it?
Darin