Thanks you all for your enthousiasm and comments !
I followed your advise and took appart my Luger and look for a manufacture date... It's an October 1940 production (10.40.) as you said it !
But Oh surprise ! when looking with a magnifier I found many other stamps :
All the in-side parts of the Luger are stamped "CN+" (+ = Swiss cross) except the trigger stamped "CW" and the coupling link stamped "CG+".
Under the center toggle link is another "CN+" and an "S" into a circle....
Could those stamps be related to the person who build those parts ?
I found another beautiful stamp inside the bottom back of the main frame (behind the recoil spring lever) and on a bottom side of the reciever are a kind of "N" with a riffle with baionet thru it... I made a fast drawing of it :

I will try to make some pictures and post it for you.
This weekend in Lausanne (city near Geneva, Switzerland) there is a fire-arms trade fair (http://www.bourseauxarmes.ch/) and I will look after the Luger tool and some wooden grip panels... If any of you are looking for something special, I'll be glad to have a look and put you in contact with a provider... ?
Best regards,
Robby