On the gilt silver models even good fakes give themselves away in the details. The serial number should be laser-marked, which means it looks grey and sits only on the surface; if it appears engraved and cut deeply into the metal, that argues against an original. Second, the workmanship at the cap top: on a Montblanc the transition between cap top, clip and cap is crisply executed, and grooves that are too deep or fits that are not quite true do not occur there. Third, the guilloché pattern — on the original's line guilloché it runs out in a particular way where it meets the cap top, and any deviation is a clear warning sign. Rings in a colour that does not match the rest of the gilding, silver-coloured rings on an otherwise uniformly gilt vermeil pen for instance, correspond to no catalogue version either; and an “Ag 925” hallmark on its own proves nothing.
Only the manufacturer can give a binding verdict, because the fakes have become so good that you often have to hold one in your hand to recognise it — from photographs even experienced collectors frequently cannot say for certain. Montblanc examines pens sent in to Hamburg for a flat fee covering return postage and the written opinion; it stood at 61 euros (as of 2016). When buying through online marketplaces, a payment method with buyer protection pays for itself: sellers passing on a collection they have bought in often have no idea themselves that a pen is fake, and will refund the purchase price.