Okay eveyrone, don't even think about going there. I tried a Google search on this but got nowhere...
Most of the folks on this board know that number as the Vehicle Identification Number (VIN). It may be called something different elsewhere in the world.
It is possible that your chassis number (VIN) is covered by a rust-inhibiting material that was applied at the dealer before your SJ was originally sold to it's first owner.
It is also possible that the VIN is stamped on the opposite side of the frame from where you looked.
My limited knowledge of production-line efficiency makes me think that, now matter where the final destination of the truck is (left-hand or right-hand drive country) it's cheaper to stamp the VIN in the same place for all of them. I could be wrong on this - it has been known to happen!
I hope that this helps!