One of my 51's ( rolled gold cap and brownish-red cap, 'semi- hooded' nib- is it a 51?) has a curious indentation at the tip of the cap. Is there a jewel missing? It also has a small white 'M' on the barrel. Though my main concern is the imaginary/missing jewel, can someone explain the 'M'?
* The 'M' is a bit smaller than you see it typed on the screen.
