The commonest signs concern the rings, the number and the clip. The cap and barrel rings of the fakes show the characteristic notches, and the serial number is punched rather than cleanly laser-engraved, often so crudely that it is hard to make out even with a loupe. The Montblanc Meisterstück lettering on the centre cap ring is frequently poorly legible too. Another point to check is where the clip sits, which on copies starts too low down, below the cap ring. And if the pen looks, by its girth, like a size 162 rollerball, the cap ought to screw on; a cap that merely pushes on argues against an original.
The frequently heard claim that such pieces are special versions for the Asian market is untrue. Montblanc never issued editions of that kind, and Far Eastern-looking motifs such as dragon ornament on a supposed Meisterstück are in themselves enough to rule out an original. In China copies like these cost one to two euros around 2013; at auction they fetched many times that.
Before bidding it is worth approaching the seller and agreeing a right of return; many sellers do not themselves know what they are selling and will go along with it. Good seller ratings say nothing about authenticity, and a strikingly low hammer price is more a warning sign than a stroke of luck.