welcome to TFL
The markings are called "proof marks" and are stamped on the gun to show it has passed certain proof tests (like not blowing up when fired, etc) required by various nations (European, primarily) before the gun can be sold or exported.
I don't know of any way to date the manufacture, sorry.
ASM usually refers to Armi San Marco, an Italian firm that made replica firearms from the 1960s through the 1990s and went out of business about 2004.
My personal experience with their guns is that they are well finished, (some very well finished) on the outside, but mechanically they are a crapshoot, and the one I had was crap. I do not recommend them for anything but static display (they can be very pretty) but if you want a shooter, you are better off with a gun from someone else.