At the risk of stirring the argument, the original post wanted the chassis number to get spare parts. Davren said its also called the VIN number and that it started ZFA...
You are both correct in what you say. The full VIN does indeed start ZFA (the international code for Fiat), and will continue with 169000 -- the model code that identifies it as a Panda.
But the chassis number -- the bit that is unique to each bodyshell -- is only the second part of the whole VIN number. This is an eight-digit number, which will only be numbers (the first two of which are likely to be zero), as hmallet said. It is only this eight digit number that the parts dept need to be sure to supply the correct parts.
If you feel so inclined, see page 252 of the vehicle's instruction book, where Fiat themselves say that the plate is in the boot (wrongly, they say its on the right!) -- and explain that it shows the model number (ZFA 169000) and the chassis number.