Not sure Gianvittorio. There is a PVD model, else I would expect it just to be in the "usual" place between the lugs at 6 o'clock. On other PVD models, the serial number tends to get moved either to the caseback or internally - not sure what happens on the Montreal, or even if it's on the same place on the PVD, steel and gold plate watches... there's a lot of metal real estate on a Montreal where you could put a number!

I suspect the answer is probably quite simple, but we need a Montreal owner to confirm - Arno has quite a few, but his book doesn't mention where the serials are...