Quoted:
how can I tell if that is a mark 1 or mark 2 ?!
There isn't a "Mark I".
In the beginning.................
There was the "standard" model. It wasn't called that because there was really only one model with several variations. The first HP featured tangent style sights because it was intended for use as a pistol/carbine and came with a detachable stock/holster combo.
The basic HP didn't change much from 1935 until the early '80's with the introduction of the MkII. The MkII differed from the Standard HP in that it featured:
-higher profile front sight, rather than the small "half moon" sight.
- a "rib" running the length of the slide between the front and rear sights
-an improved feed ramp. the original HP had a "humped" ramp that worked fine with FMJ, but could cause problems with some of the new hollow point 9mm rounds that started becoming popular in the early '80's.
-a "drain hole" at the muzzle end of the slide.
-Parkerized finish instead of the highly polished blue. Some came out a gray-green, others gray-black and some coal black.
Early MkII's had the tiny thumb safety, later MkII's had the larger ambi safeties.
The MkIII introduced dovetailed sights and later the cast frame.